Gravitational and magnetic surveys involve the use of portable units which are easily transported using light ground vehicles or by light aircraft. Off-road vehicle travel is common in these two types of surveys and on some surveys there is minor surface disturbance when small hand dug holes are used for instrument placement along survey lines.

Reflection seismologic surveys are frequently employed by the exploration geologist because these surveys can provide the largest amount of subsurface data. This type of survey involves the collection of subsurface geological information by recording the impulses from an artificially generated shock wave. On land, this would begin with the creation of a shock wave and the recording, as a function of time, the reflected seismic energy as it arrives at the vibration detectors, or geophones. The geophones are one-half to five pound seismometers which are placed on the ground at set intervals and are connected to a recorder truck that receives and records the reflected seismic energy.

The vibration detectors and shock wave generator would be located along lines on a one or two mile grid. Surveys may be laid out in excess of 40 miles in a series of grid patterns or in a single line. Seismic operations are conducted on existing roads where possible but, the clearing of vegetation and rocks may be required to improve access for seismic source and recording trucks. Completely clearing a seismic line of vegetation is unusual and most lines are not bladed except at drainage crossings. In some rough or sandy areas it may be necessary to use a bulldozer to pull the seismic trucks through the difficult spots.

In remote areas where there is little known subsurface data, a series of short seismic lines may be required to determine the characteristics of the subsurface formation. After this, seismic lines would be aligned to make seismic interpretations more accurate. Although alignment may be fairly critical, spacing of the lines can often be changed up to a quarter mile on a one mile grid before the results will affect the investigation program.

Seismic methods are usually classified by the various methods of generating the shock wave. These methods include: 1) Thumper, 2) Vibrator, 3) Spark Ignition, 4) Surface Explosive, 5) Subsurface Explosive.

The thumper method involves dropping a three ton steel slab to the ground many times in succession along a predetermined line.

The vibrator method is widely used and is replacing the explosive methods in areas where vehicle access is not difficult. An operation of this type would use three or four large vibrator trucks, four or five support vehicles, and a crew of ten to fifteen people. The four foot square vibrator pads are lowered to the ground and the vibrators on all trucks are then operated electronically from the recording truck. After the reflections are recorded the trucks move forward a short distance and the process is repeated.

The spark ignition method can be used with a variety of vehicles and consists of a bell shaped chamber mounted underneath the vehicle. The shock wave is generated by the spark ignition of a propane and oxygen mixture and is imparted to the ground through the bell shaped chamber. This method causes little surface damage.

The thumper, vibrator, and spark ignition methods all have surface disturbing factors in common. Generally, these methods involve the use of existing roads or cross-country travel by four or five energy source trucks (usually weighing to one and one-half to ten tons) plus the recording truck, cable trucks, or pickup trucks. Bulldozer assistance may be required to cross drainages or to traverse steep terrain. The vehicles may travel off road along a single trail made by the trucks as the survey progresses. The vehicles may make several parallel trails in an attempt to distribute travel loads over a broader area. Travel along the line is usually a matter of one to two passes by the vehicle since the energy source is mobile and recording is done as the vehicles move down the line.

Historically, both subsurface and surface explosive methods have been the most widely used process to generate shock waves. In the subsurface method, five to fifty pounds of explosive charge are detonated at the bottom of a twenty-five to two hundred foot deep drill hole. These drill holes are usually two to six inches in diameter and drilled with a truck mounted drill. Detonation of the charge in some areas causes no surface disturbance, while in other areas, a small crater up to six feet in diameter is created. The same hole may be reloaded and shot several times to find the depth and charge returning the best signal. Cuttings from the well are normally scattered by hand near the shot hole, or put back in the shot hole after detonation. Bentonite mud is often used to plug the shot hole after the survey is completed.

The trucks used while conducting explosive seismic methods are similar to the trucks used in thumper and vibrator methods except that the trucks used to transport the drill are much heavier (15 to 20 tons). As with other truck transportation operations, existing roads may be used or trails may be blazed by the drill or bulldozer. A truck mounted drill and shot operation generally takes longer to complete and requires more trips by drill service vehicles than do vibrator and thumper operations.

In areas where there are limitations, steep topography, or other restraints prevent use of truck mounted drill rigs or recording trucks, light weight portable drill equipment can be used. Various kinds of portable drills can be backpacked or delivered by helicopter to the study area. These portable operations use a pattern of holes drilled to a depth of about 25 feet, the holes are then loaded with explosives and detonated simultaneously.

The surface explosive charge method involves the placing of explosives directly on ground, on snow, or on a variety of stakes and platforms including paper cones, survey stakes, lathes, or 2x4 wooden posts up to eight feet high. For this reason, surface explosive methods are very mobile and can be transported using 4X4 vehicles or adapted to airborne or ground pack teams.

A given area may be explored several times by the same or different companies over a long period of time using one or more of the geophysical methods mentioned above. This multiple exploration may be undertaken because the initial attempts were unsuccessful, another company wants its own information, or new and different techniques and/or equipment are used.

Generally, access roads are bladed 12 to 14 feet wide and are not crowned or ditched. Under certain conditions it may only be necessary to brush the access route to clear vegetation. Other roads may require road cuts in excess of 20 feet and fills of more than 10 feet. Stratigraphic tests that require large amounts of surface disturbance are unusual since construction costs may outweigh the value of the information gained.

The average drill site requires an area of one-half acre or less surface disturbance in order to position the drill and support equipment. If high pressure air is used to circulate the rock chips, dust may be emitted to the air when samples are collected. If mud is used as a drilling fluid, mud pits may be dug but, it is more common to use portable mud tanks. Usually one to three days is required to drill the test holes, depending on depth to and hardness of the bedrock. In areas with shallow, high-pressure, water bearing zones, casing may be required to prevent water from entering the hole.

After the surface and subsurface geological studies, the seismic, and other geophysical surveys, comes the evaluation of the prospect. Only by drilling a wildcat well (a well drilled in unproved territory) will the oil company know if the rocks in the prospect they have identified contain oil or gas. Nationally, one in 16 wildcat wells produces significant amounts of oil or gas. The deeper wildcat wells may require several months or more to complete; shallower wells up to a few thousand feet deep may be completed in as little as a few weeks. The deeper the test, the larger the drilling rig and the longer the drilling time required. Prior to approval of drilling, on-site inspections are conducted with the proposed drill pad and access road staked out, to assess potential impacts and attach appropriate mitigations to the permit to drill. A drill pad from one to four acres in size is then cleared of all vegetation, and leveled for the drill rig, mud pumps, mud (or reserve) pit, generators, pipe rack, and tool house. Topsoil and native vegetation are removed and stockpiled for use in the reclamation process. The mud pit may be lined with plastic or bentonite to prevent fluid loss or prevent contamination of water resources. Other facilities such as storage tanks for water and fuel are located on the pad or are positioned nearby on a separate cleared area. If the well site is not large enough for the equipment required to rig-up (prepare the drilling rig for operation), a separate staging area may be constructed. Staging areas are usually no larger than 200 feet by 200 feet and may only require a wide flat spot along the access road on which vehicles and equipment are parked.

Five thousand to 15,000 gallons of water per day may be needed for mixing drilling mud, cleaning equipment, cooling engines, etc. A surface pipeline may be laid to a stream or a water/well, or the water may be trucked to the site from ponds or streams in the area.

The drill rigs are very large and may be moved in pieces. In some instances, rigs can be moved short distances on level terrain with little or no dismantling of equipment which will shorten the tearing-down and rigging-up time. Moving a dismantled rig involves use if heavy trucking equipment for transportation, and crews to erect the rig. Gross weight of vehicles may run in excess of 80,000 lbs.

In order to move a drill rig and well service equipment from one site to another, and to allow access to each site, temporary roads may be built. These roads are generally 16 feet to 18 feet wide (driving surface) and may be as short as 200 feet or as long as ten miles or more. Bulldozers, graders and other types of heavy equipment are used to construct and maintain temporary wildcat roads.

The start of a well is called “spudding in” and, this procedure is started by forcing a short piece of tubing called conductor pipe into the ground and cementing it in place. This prevents surface sand and dirt from sloughing into the well hole. Next the regular drill bit and drill string (the column of drill pipe) are then used. These pass vertically through a heavy steel turn table (the rotary table), the derrick floor and the conductor pipe. The rotary table is geared to one or more engines, and rotates the drill string and bit. As the bit bores deeper into the earth, the drill string is lengthened by adding more pipe to the upper end.

Once the hole reaches a depth below the groundwater zones another string of pipe (the surface casing) is set inside the conductor pipe and cemented in place by pumping cement between the casing and the borehole wall. Surface casing acts as a safety device to protect fresh water from drilling fluid contamination. Blowout preventors (large metal rams) are installed around the surface casing just below the derrick floor to prevent the well from “blowing out” in the event that the drill bit encounters a high pressure zone. In an emergency, these rams would be activated and the rams would close around the drill string and seal the well.

After setting the surface casing, drilling resumes using a smaller diameter bit. Depending on well conditions, additional strings of casings (intermediate casing) may be installed before the well reaches the total depth. During drilling, a mixture of water, clay and chemical additives known as “mud” are continuously pumped down the drill pipe. The mud exits through holes in the bit and returns to the surface outside the drill-pipe. As the mud circulates, it cleans and cools the bit and carries the rock chips (cuttings) to the surface. It also helps to seal off the sides of the hole (thus preventing cave-ins), and to control the pressure of any water, gas or oil encountered by the drill bit.

The mud is the first line of defense against a blow-out since it is used to control pressure. It is for this reason that a pit full of “reserve” mud (the reserve pit) is maintained on location. The reserve mud is used in emergencies to restore the proper drilling environment when a radical or unexpected change in down-hole pressure is encountered.

The cuttings are separated from the mud and sampled so that geologists can analyze the various strata through which the bit is passing. The remainder of the cuttings passes into the reserve pit as waste. Some holes are drilled at least partially with compressed air which serves the same purpose as drilling mud of cooling and cleaning the bit and circulating the cuttings out of the hole.

During completion of drilling activity, the well is logged. This entails the use of geophysical instruments to measure the physical characteristics of the rock formations and associated fluids through which the borehole passed. These instruments are lowered to the bottom of the well, and slowly raised to the surface while recording data. Other measuring procedures include the drill stem test, in which pressures are recorded and fluid samples taken from zones of interest. After studying the data from those logs and tests, the geologist and/or petroleum engineer decide if the well will produce petroleum.

Well Stimulation may be used to enhance oil recovery. Several methods of well stimulation could be used. HF is one of these methods that is reasonably foreseeable for the leases on this sale. HF is the process of applying high pressure to a subsurface formation via a wellbore, to the extent that the pressure induces fractures in the rock. Typically the induce fractures will be propped open with a granular “proppant” to enhance fluid connection between the well and formation. The process was developed experimentally in 1947 and has been used routinely since 1950. The Society of Petroleum Engineers (SPE) estimates that over one million hydraulic fracturing procedures have been pumped in the United States and tens of thousands of horizontal wells have been drilled and hydraulically fractured. It can greatly increase the yield of a well, and development of hydraulic fracturing methods and the drilling technology in which it is applied (in particular, long wells drilled horizontally within the targets) have enabled production of oil and gas from tight formations formerly not economically feasible.

If the well did not encounter oil and gas, it is plugged with cement and abandoned. The well pad and access road are recontoured and revegetated.

If the well will produce, casing is run to the producing zone and cemented in place. A proper cementing of the production casing string is required to provide coverage and prevent interzonal communication between oil and gas horizons and usable water zones. The drill is usually replaced by a smaller rig that is used for the final phase of completing the well.

If the well is not free-flowing, it will be necessary to use pump methods. After the pump is installed, the well may be tested for days or months to see if it is economically justifiable to produce the well and to drill additional development wells, During this phase, more detailed seismic work may be run to assist in precisely locating the petroleum reservoir and to improve previous seismic work.

Spacing for both oil and gas wells is based on the characteristics of the producing zones. If oil or gas is producing from more than one formation, the surface location of the wells may be closer than one per 40 acres. Once well spacing has been approved, development of the lease proceeds. During the development stage, the road system of the area is greatly expanded. Once it is known which wells produce and the expected length of their productive life, a system of permanent roads can be designed and built. Because it often takes several years to develop a field and determine field boundaries, the permanent road system is usually built in segments. For this reason, many temporary roads (built initially for wildcats or development) end up as long term (in excess of 15 years) main access or haul roads. The planning of temporary roads for wildcats and development wells is done with road conversion to long term in mind.

Since development wells have longer life spans than wildcat wells, access roads for development wells are better planned, designed and constructed. Access roads are normally limited to one main route to serve the lease areas, with a maintained side road to each well. Upgrading of temporary roads may include ditching, draining, installing culverts, graveling, crowning, or capping the roadbed. The amount of surface area needed for roads would be similar to that for temporary roads mentioned earlier and would also be dependent on topography and loads to be transported over it. Generally, main access roads are 20 feet to 24 feet wide and side roads are 14 feet to 18 feet wide. These dimensions are for the driving surface of the road and not the maximum surface disturbance associated with ditches, cuts or fills. The difference in disturbance is simply a matter of topography. Surface disturbance in excess of 130 feet is not unusual in steep terrain (slopes exceeding 30 percent).

When an oil field is developed on the current minimum spacing pattern of 40 acres per well, the wells are 1320 feet apart in both north-south and east-west directions. If a one square mile section is developed with 16 wells, at least four miles of access roads may be increased since steep slopes, deep canyons, and unstable soil areas must often be circumvented in order to construct stable access to the wells. Surface use in a gas field may be similar to an oil field though usually less) even though the spacing of wells is usually 1600 acres. Though a 160 acre spacing requires only four wells per section, the associated pipeline system often has similar initial surface requirements (acreage of surface disturbance).

In addition to roads, other surface uses required for development drilling may include flowlines, storage tank batteries; facilities to separate oil, gas and water (separators and treaters); and injection wells for salt water disposal. Some of the facilities may be installed at each producing well site, and others at places situated to serve several wells. Surface use in an oil and gas field may be affected by unitization of the leaseholds. In many areas with federal lands, an exploratory unit is formed before a wildcat is drilled. The boundary of the unit is based on geologic data. The developers unitize the field by entering into an agreement to develop and generate it as a unit, without regard to separate ownerships. Costs and benefits are allocated according to agreed terms.

Unitization reduces the surface-use requirements because all wells are operated as though on a single lease. Duplication of field processing facilities is minimized because development operations are planned and conducted by a single unit operator, often resulting in fewer wells. The rate of development well drilling depends on whether the field is operated on an individual lease basis or unitized, the probability of profitable production, the availability of drilling equipment, protective drilling requirements (drilling requirements to protect federal land from subsurface petroleum drainage by off-setting nonfederal wells), and the degree to which limits of the field are known. The most important development rate factor may be the quality of production. If the discovery well has a high rate of production and substantial reserves, development drilling usually proceeds at a fairly rapid pace. If there is some question whether reserves are sufficient to warrant additional wells, development chilling may occur at a much slower pace. An evaluation period to observe production performance may follow between the drilling of successive wells.

Development on an individual lease basis usually proceeds more rapidly than under unitization, since each lessee must drill his own well to obtain production from the field. On a unitized basis, however, all owners within the participating area share in a well’s production regardless of upon whose lease the well is developed. Spacing requirements are not applicable to unit wells. The unit is developed on whatever the operator considers to be the optimal spacing pattern to maximize recovery. As mentioned earlier, drilling in an undeveloped part of a lease to prevent drainage of petroleum to an offset well on an adjoining lease (protective drilling) is frequently required in fields of intermingled federal and privately owned land. The terms of federal leases require such drilling if the offset well is on non-federal lands, or on federal lands leased at a lower royalty rate.

Many fields go through several development phases. A field may be considered fully developed and produce for several years, then a well may be drilled to a deeper pay zone. Discovery of a new pay zone in an existing field is a “pool” discovery, as distinguished from a new field discovery. A pool discovery may lead to the drilling of additional wells with the bore holes separated only by feet or inches. Existing wells may also be drilled deeper.

Usually four to six inch diameter pipelines transport the petroleum between the well, the treating and separating facilities, and central collection points. These lines can be on the surface, buried, or elevated. Most pipelines are buried.

Trucking and pipeline are the two methods used separately or in conjunction to transport oil out of a lease or unitized area. Trucking is used to transport crude oil from small fields where installation of pipelines is not economical and the natural gas in the field is not economically marketable.

Pipelines are the most common way to transport oil and gas. If a field has substantial amounts of natural gas, separate pipelines will be necessary for oil and gas. Pipelines move the oil from gathering stations to refineries. As existing fields increase production or new fields begin production, new pipelines may be needed. These new lines usually vary in size from four to 16 inches in diameter, and range in length from a few miles (to tie into an existing pipeline), to hundreds of miles to supply a refinery. Construction of a pipeline requires excavating and hauling equipment, a temporary and/or permanent road, possibly pumping stations, clearing the right-of-way of vegetation and possibly blasting.

Natural gas pipelines transport gas from the wells (gathering or flow lines) to a trunk line then to the main transmission line from the area. Flow lines are usually two inches to four inches in diameter and mayor may not be buried. Trunk lines are generally six inches to eight inches in diameter and are buried, as are transmission lines which vary in diameter from ten inches to 36 inches. The area required to construct a pipeline varies from about 15 inches wide (for a two inch to four inch surface line) to greater than 75 feet for the larger diameter transmission lines (24 inches to 36 inches). Surface disturbance is primarily dependent on size of the line and topography of the area on which the line is being constructed.

Compressor stations may be necessary to increase production pressure to the same level as pipeline pressure. The stations vary in size from approximately one acre to as much as twenty acres for a very large compressor system. Construction techniques for natural gas lines are similar to those used for oil pipelines.

Production in an oil field begins just after the discovery well is completed and is usually concurrent with development operations. Temporary facilities may be used at first, but as development proceeds and reservoir limits are determined, permanent facilities are installed. The extent of such facilities are dictated by the number of producing wells, expected production, volume of gas and water produced with the oil, the number of leases, and whether the field is to be developed on a unitized basis.

The primary means of removing oil from a well is by the use of pumping jacks. The pumps are powered by electric motors (power lines required) or if there is sufficient casing head gas (natural gas produced with the pumped oil), or another gas source is available, it may be used to fuel internal combustion engines.

Some wells may produce sufficient water that must be disposed of during operation of the well. Although most produced waters are brackish to highly saline, some are fresh enough for beneficial use. If water is to be discharged, it must meet certain water quality standards. Because water may not come from the treating and separating facilities completely free of oil, oil skimmer pits may be established between separating facilities and surface discharge.

When salt water is disposed of underground, it is always introduced into a formation containing water of equal or poorer quality .It may be injected into the producing zone from which it came or into other producing zones. In some cases, it could reduce the field productivity and may be prohibited by state regulation or mutual agreement of operators. In some fields, dry holes or depleted producing wells are used for salt water disposal, but occasionally new wells are drilled for disposal purposes. Cement is squeezed between the casing and sides of the well to prevent the salt water from migrating up or down from the injection zone into other formations.

Underground oil is under pressure in practically all reservoirs. This pressure is usually transmitted to the oil through gas or water in the reservoirs with the oil. When oil is pumped out of the well, pressure is reduced in the reservoir around the drill hole. This allows the gas or water in the reservoir to push more oil into the space next to the well. A reservoir that has mostly gas pushing the oil is called “gas drive”, and one that has mostly water pushing the oil is called “water drive”. Oil that is recovered under these natural pressures is considered primary production. Primary production accounts for about 25 percent of the oil in a reservoir.

Methods of increasing recovery from reservoirs generally involve pumping additional water or gas into the reservoir to maintain or increase the reservoir pressure. This process is called secondary recovery. Recently, the trend has been to institute secondary recovery processes very early in the development of a field. Surface disturbance from a water flooding recovery system is similar to drilling and development of an oil and gas well itself, i.e., a drill pad and access road are constructed and water pipelines may be built. Surface use is increased substantially since as many as four injection wells may be used for each oil well in the field (there are many different patterns as well as many other methods of secondary recovery).

Tertiary recovery methods increase recovery rates by lowering the viscosity of the oil either by heating it or by injecting chemicals into the reservoir so that the oil flows more easily. Heating of reservoir oil can be accomplished by injecting steam into the reservoir. Tertiary recovery methods are not yet widely used in the EDO. Recovery (including secondary and tertiary recovery) from any given oil reservoir is expected to average 40 percent nationally.

Crude oil is usually transferred from the wells to tank storage facilities (tank battery) before it is transported from the lease. If it contains gas and water, they are separated before the oil is stored in the tank battery .The treating and separating facilities are usually located at a storage tank battery on or near the well site.

After the oil, gas, and water are separated, the oil is piped to storage tanks located on or near the lease. There are normally at least two tanks; so that one tank can be filling as the contents of the other is measured, sold, and transported. The number and size of tanks vary with the rate of production on the lease, and with the extent of automation in gauging the volume and sampling the quality of the tank’s contents.

The life span of fields varies because of the unique characteristics, the nature of the petroleum, subsurface geology, and political, economic, and environmental constraints. All affect a field’s life span from discovery to abandonment. The life of a typical field is 15 to 25 years. Abandonment of individual wells may start early in a field’s life and reach a maximum when the field is depleted.

Well plugging and abandonment requirements vary with the rock formations, subsurface water, well-site, and the well. In all cases, the formations bearing usable-quality water, oil, gas or geothermal resources, and/or prospectively valuable deposits of minerals will be protected.

Generally, in dry wells, the hole below the casing is filled with heavy drilling mud, a cement plug is installed at the bottom of the casing, the casing is filled with heavy drilling mud, and a cement cap is installed on top. A pipe monument giving the location, lease number, operator, and name of the well is required unless waived by the Authorized Officer. If waived, the casing may be cut off and capped below ground level. Protection of aquifers and known oil and gas producing formations may require placement of additional cement plugs.

In some cases, wells that formerly produced are plugged as soon as they are depleted. In other cases, depleted wells are not plugged immediately but are allowed to stand idle for possible later use in a secondary recovery program. Truck-mounted equipment is used to plug former producing wells. In addition to the measures required for a dry hole, plugging of a depleted- producing well requires a cement plug in the perforated section in the producing zone. If the casing is salvaged, a cement plug is put across the casing stub. The cement pump-jack foundations are removed or buried below ground level. Surface flow and injection lines are removed, but buried pipelines are usually left in place and plugged at intervals as a safety measure.

After plugging, the drilling rig is removed and the surface, including the reserve mud pit, and the well pad area is restored to the requirements of the surface management agency. This may involve the use of bulldozers and graders to recontour those disturbed areas associated with the drill pad plus the access road to the particular pad. The reserve pit (the part of the mud pit in which a reserve supply of drilling fluid and/or water is stored) must be evaporated or pumped dry, and filled with soil material stockpiled where the site was prepared. There is little leakage if the pit was lined with plastic or bentonite. The area is reshaped to a useful layout that will allow revegetation to take place, the landform is restored as near as possible to its original contour, and erosion minimized. After grading the subsoil and spreading of the stockpiled topsoil, the site is seeded with a grass mixture that will establish a good growth. A fence may be erected to protect the site until revegetation is complete, particularly in livestock concentration areas.