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EXPLORING FOR OIL AND GAS The earliest access to oil and gas was through surface such as Canada, tar sands are mined similarly to the expressions. Shallow deposits, along with shallow way coal and metal ores are mined. Today, however, faulting, allowed oil and gas to migrate to the surface almost all commercial oil and gas exploration is from of the land. Societies have accessed oil and gas for wells many thousands of feet deep. (Daniel Yergin, millennia. The Bible, for example, records Noah The Prize: The Epic Quest for Oil, Money and Power, covering the ark with pitch. Similarly, Moses was Free Press, New York, 1990) delivered from death in a basket coated with tar and pitch. Historians believe that the Chinese drilled brine Conventional oil and gas deposits, as opposed to resource plays such as shale oil and gas, are located in (notmodern oil and oil well, gas) drilledwells as by early “Colonel” as 2000 Edwin B.C. TheDrake first permeable rocks, such as sandstone, and are held in near Titusville, Pennsylvania, in 1859 was placed place by a trap. A trap is simply a means of preventing near oil seeps, which were known to both Native further migration of the oil or gas. Four simple traps Americans and European settlers. In some regions, are illustrated (FIGURE 1). FIGURE 1. OIL AND GAS NATURAL GAS TRAPS OIL NATURAL OIL GAS FAULT ANTICLINE TRAP FAULT TRAP FAULT SALT DOME NATURAL NATURAL OIL GAS OIL GAS OIL TRAPS ON SALT DOME FLANKS STRATIGRAPHC TRAP 2 FIGURE 2. SEISMIC SURVEY RECEIVERS RECEIVERS SOURCE A development team, consisting of geoscientists specially equipped to provide the vibrational and engineers, will study the subsurface, consider energy (FIGURE 2). development options, and make recommendations on the locations and number of wells to develop After interpretation of the subsurface survey and creation of an exploration or a development plan, ateam particular may use reservoir is a seismic or field. survey. One Sound tool that waves the are one or more wells will be designed. Depending on the development, preparations to drill may be the introduced into the ground, and their reflections are recorded“picture” ofat the subsurfacesurface. From can these be developed reflections, in mucha firstbe cleared activities and visible a drilling in an rig area. assembled A location at the (pad) site. will the same way a sonogram is used to look deeply Rig operators will drill the well. The most dominant within a human patient. Seismic energy, once applied feature of the rig is the derrick, the tall structural with dynamite, is more often applied through a truck piece visible from far away. It raises and lowers the drill pipe, and later, the casing into the well. SOUTHERN EXTENSION RISK MANAGEMENT EDUCATION BLACK WARRIOR PROJECT 3 The drill pipe is stored in the derrick in “stands” of for power. Also in the derrick are a crown block pipe, usually three 30-foot joints, resulting in 90-foot (stationary at the top of the derrick) and a traveling stands. As the well deepens, more and more drill block to raise and lower drill pipe and casing. The rig pipe is needed (FIGURE 3) will also have a means for rotating the pipe, either surface is the drill bit. It is. Out larger of sight than tothe those drill onpipe the a kelly or a top drive. Underneath the derrick is the and creates a hole the diameter of the bit. Drilling substructure, which allows room for another critical fluid,down oftenthe drill referred pipe, pastto as thedrilling bit, and mud, back is pumped up the pieceIf the drillingof equipment, mud fails the for blow-out any reason preventer to contain (BOP). the circular space between the pipe and the hole. The mud cools and lubricates the bit, cleans the hole of well fluids, the BOP can be closed to secure the well drill cuttings, and provides the hydrostatic pressure and allow operators to introduce mud of sufficient densitycontain topipe contain rams theto close well andfluids. seal Systems around vary, the drill but all toand contain pumps, all along of the with fluids equipment in the formation. to clean andMud treat tanks pipe, along with blind rams that will seal off the the mud are also on location, along with generators entire wellbore. FIGURE 3. DRILLING RIG DRILLING RIG COMPONENTS DRILL PIPE ENGINES MUD PUMPS BLOW-OUT PREVENTERS 4 FIGURE 4. WELL CASING STRINGS CONDUCTOR SURFACE CASING INTERMEDIATE CASING PRODUCTION CASING The well itself consists of a series of concentric holes, each isolated by casing (usually steel) and cement enoughhole section to continue with a bitdrilling. that passes Operators through drill the the surface next (FIGURE 4) casing. This hole may be the last one drilled, or more conductor,. Thewhich first, is structuraland largest rather diameter, than casingpressure- is the intermediate holes may be needed, as determined by containing. It may be driven or cemented in place. Its the well design. role is to carry the load of the rest of the equipment used in the drilling process. It is analogous to the Each additional casing string is run and cemented, foundation of a building. Operators use a bit to drill a withthe well. sufficient Cement cement is usually to provide pumped, zonal much isolation like the in holesection that is passesthen cased through off with the conductor. casing and This cemented first hole to drilling mud, down the casing and back up the hole. surface—a process referred to as the surface casing. Additional equipment is run in the casing string to Its two main roles are to protect fresh water aquifers facilitate good cementing. and to isolate the rest of the well from shallow, weak rocks. After the cement is cured, operators prepare to drill the next hole section. They pressure test the Theusually final penetrates step is the the production producing casing formation. string, Most which casing and then drill and pressure test a few feet often, explosive jet perforations will penetrate the of formation to ensure that the formation is strong casing and cement and allow access to the formation SOUTHERN EXTENSION RISK MANAGEMENT EDUCATION BLACK WARRIOR PROJECT 5 for treatment and production. In all cases, the casing Every Representative, Environmentalist, Regulator, is cemented to seal and separate the producing Reporter, Investor, University Researcher, Neighbor and formation from other intervals in the well. For all Engineer Should Know About Estimating Frac Risk and Improving Frac Performance in Unconventional Gas casing strings, Mississippi Oil and Gas Board rules and Oil Wells, SPE 152596, 2012). requireand/or intothe preventionsources of drinkingof fluid migration water. out of zone Most conventional treatments consist of the Hydraulic Fracturing following stages. First, operators pump a pad, whichproppant is the added. base Hydraulic hydraulic fracturefracturing treatments fluid with of no Aexceeds hydraulic the fracturefracture occursinitiation when pressure the fluid of thepressure rock. Such fractures can occur naturally. In oil and gas conventional reservoirs typically use a fluid that is gelled (viscosified) with an organic starch, generally production, hydraulic fracturing can occur when fluid a guar-based fluid. Shale oil and gas plays often use isdue pumped to low intorock apermeability, well at sufficiently to crack high the pressure, rock open. low-viscositypolymers added fluids to reduce known friction as slick rather water, thanwhich to has Proppant (sand or man-made materials) is pumped carry large proppant loads. The pad has two basic purposes: (1) it creates the hydraulic fracture; and into the cracks to hold them open. The resulting flow path is preferable to the well fluids,(FIGURE resulting 5). in a (2) it controls fluid loss to the formation so that the stimulated (higher flow rate) well fracturing job can be carried out efficiently. The next stage or stages contain the proppant. In The first hydraulic fracturing treatments were conventional fracturing, the designer will usually performed by Stanolind Oil and Gas in 1947. The build what is called a ramping schedule, beginning process was thenA commercialized Hydraulic Process by forHalliburton Increasing in with low concentrations of proppant and building 1949the Productivity (Clark, J. B, of Wells, Petroleum Transactions, tohelps the ensurefinal, higher that coverage proppant of loading. the fracture This schedulewith AIME,Petroleum January, Engineers 1949). estimated In 2010, the that Society 2.5 million of proppant is complete and as even as possible. The hydraulic fracture treatments had been performed productivity increase from the hydraulic fracture worldwide, with more than a million in the U.S. depends on achieving the desired proppant loading in Hydraulic Fracturing 101: What alone (King, George, 6 various proppants, from sand to ceramics and the fracture. The final stage is the displacement stage; bauxite. For the most part, the designer chooses the i.e., pushing the proppant-laden fluid down to the lowest-cost proppant that will deliver the needed formation and leaving clean fluid in the wellbore. conductivity. At high earth stresses, sand grains may The key to a good hydraulic fracture treatment is be crushed and lose permeability. In those cases, the obtaining a high permeability path through which designer may opt for the more expensive man-made proppants. well fluids can travel into the wellbore. There are FIGURE 5. CONVENTIONAL HYDRAULIC FRACTURE PLANE SOUTHERN EXTENSION RISK MANAGEMENT EDUCATION BLACK WARRIOR PROJECT 7 FIGURE 6. VERTICAL AND HORIZONTAL WELLS FRESH WATER TARGET FORMATION In conventional reservoirs, shale provides the smaller surface footprint. That is, more oil and gas reservoir seal due to its extremely low permeability. resources can be accessed with less land usage. In shale plays, however, hydraulic fracturing is often Well Integrity and Fracture usedthese in very combination tight rocks with (FIGURE horizontal 6).

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