Understanding Shale Reservoirs: Characteristics, Recovery, and Fracturing Techniques, Exams of Environmental Science

Download Understanding Shale Reservoirs: Characteristics, Recovery, and Fracturing Techniques and more Exams Environmental Science in PDF only on Docsity! LSU PETE 4190 Midterm review solution guide all complete exam new update Louisiana State University In today's industry, the term ______ is typically used to describe any fine - grain sedimentary rock that require massive stimulation for economic recovery. shale In today's industry, the term "shale" is typically used to describe any _________________________________________________ fine - grain sedimentary rock that require massive stimulation for economic recovery. In today's industry, the term "shale" is typically used to describe any fine - grain sedimentary rock that require massive stimulation for economic recovery. In this terminology shale rock may be composed of ____________ (smectite, illite, chlorite, kaolinite), quartz, feldspar, and carbonates. clay minerals In shales, ______ content varies between ~10 to 70% in these plays while the rest is _____ and ______. clay quartz carbonates For which of the following rock mineralogy is more important? A. High permeability conventional reservoir B. Ultra-low permeability shale reservoir Ultra-low permeability shale reservoir The mineralogy of shale rocks is very important for hydrocarbon recovery because rocks with less clay and more quartz and carbonates are more ______ and potentially comprised of _______________. brittle, larger pores More brittle rocks are ______ to fracture in hydraulic fracturing stimulation compared to ductile/deformable rocks. easier Many shale reservoirs are petroleum _____________, mainly characterized by low permeability less than 1 micro Darcy (µD). source rocks Many shale reservoirs are petroleum source rocks, mainly characterized by ___________________ less than 1 micro Darcy (µD). low permeability _____________________ (which are not source rocks) with permeabilities below 0.1 mD are also often categorized under shale reservoirs due to their need for extensive hydraulic fracturing to achieve economic production. Tight reservoirs Tight reservoirs (which are not source rocks) with permeabilities below 0.1 mD are also often categorized under ___________________ due to their need for extensive hydraulic fracturing to achieve economic production. shale reservoirs In short, the "shale" terms is more about the _____________ and extraction technology than the rock type and mineralogy. grain size In _____________ Mitchel Energy invested in shale. They drilled vertical wells and applied massive hydraulic fracturing. early 1980's Natural gas production from shale started to rise in the _____________ early 2000s Liquid-rich shales were more difficult to develop. Innovative fracture design in the Bakken, Eagle Ford, and Permian in _____________ resulted in significant production improvements. 2008-2012 Primary recovery factor of tight oil is ________ thermogenic The remaining kerogen above 180° C will be very rich in carbon and in solid state known as ______. coal The temperature for oil to be generated at source rock is: A. 30 to 60 °C B. 60 to 120 °C C. 120 to 180 °C D. 180 to 230 °C 60 to 120 °C The rock in which the organic matter turns into oil and gas is referred to as ___________ source rock The source rock has a very __________________ which enables it to retain the oil and gas generated in it for millions of years low permeability Burial of the source rock under kilometers of overlying sediments combined with the generation of lower density oil and gas causes the pressure in the source rock to significantly increase. As a result, the source rock cracks allowing oil and gas to _____________________ to overlying permeable formations. migrate upward Upward migration of oil and gas may continue all the way to the surface creating oil and gas ______________. seepages migrating oil and gas may be stopped by an impermeable layer, also known as a __________ caprock Migrating oil and gas may be stopped by an impermeable layer (caprock). The oil/gas then migrates updip along the caprock until it can no longer travel further updip e.g. because of encountering crest of an anticline or a sealing fault. The resulting accumulation of oil and gas in such a structure creates the ________________________. conventional reservoirs Tens of kilometers of migration is common for oil and gas to migrate from the source rock to the reservoir rock A. True B. False True Conventional ultimate oil reserves are _____________________ - by including world oil consumption of 1.360 Tbbls to date and 1.7 Tbbls of global proved reserves. ~3 trillion bbls (Tbbls) While, hydraulic fracture technology works in the US, it may not work in other parts of the world especially in arid or semi-arid regions with water access problems. A. True B. False True Permeability is proportional to grain size. That is, finer grains means lower permeability A. True B. False True Roughly ______ percent of hydrocarbons remain in the source rock 50 Roughly 50 percent of hydrocarbons remain in the source rock. Out of the remaining 50% that migrates, _____ percent makes it to a conventional reservoir and ______ percent is lost (usually at the surface, ex: seepages) 5%, 45% The 5% of hydrocarbons that get trapped in conventional reservoirs are referred to as _______________________________ petroleum system yield (5%) The hydrocarbon resources in shale are 10 times those in conventional reservoirs. A. True B. False True Assuming recovery factors of 10% for shale and 33% for conventional reservoirs, the hydrocarbon reserves in shale are 3 times larger than those in conventional reservoirs. A. True B. False True Conventional (7.5)(0.33) = 2.5 Unconventional (75)(.1) = 7.5 ________________ reservoirs are concentrated oil and gas accumulations in high quality rocks (permeability in the range of mD to D) accommodated by a combination of natural forces including compaction, pressurizing, gravity, and structural trapping. conventional Conventional reservoirs are sparse, occur over relatively small areas (generally hundreds of square kilometers), and their boundaries are well constrained. A. True B. False True Unconventional shale reservoirs are hydrocarbon resources to be accessed in source rocks. A. True B. False True With a mix of very fine grains of clay, sand, and carbonates, shales are characterized by very low permeabilities in the range of ________________ 10-1000 nano Darcy (nD) Similar to conventional reservoirs, gravity plays a role in distribution of fluids in unconventional reservoirs. A. True B. False False (fluid distribution is controlled by depth at which the fluid was generated) The fluid distribution in unconventional reservoirs is controlled by the __________ at which the fluid was generated. As such, the fluid changes from heavy oil to light oil to condensate to gas as depth is increased. depth Hydrocarbon presence in shale source rocks is not constrained by the structural trapping required in conventional reservoirs. The initial reservoir pressure located at 5000 ft depth is 5000 psia. The reservoir is abnormally pressured. A. True B. False True (0.433*5000 = 2200 psi) Before introduction of massive fracturing of horizontal wells, it was not technically and economically feasible to produce most shale resources implying reserves were essentially zero. A. True B. False True Drilling process in shale reservoirs is very _______ to conventional well drilling. One significant difference is the sheer magnitude of the required drilling. similar A well can drain a much smaller area in a shale well compared to conventional well A. True B. False True ______________, sometimes called multi-well pad drilling, is a drilling practice that allows multiple wellbores to be drilled from a single, compact piece of land known as a pad. Pad drilling Well pads are considerably _________ than building sites for individual wells and connecting them with flow lines and roads. cheaper Well pads also significantly reduce the environmental footprint of drilling, completion, and production operations, allowing the land to be sustainably used for multiple purposes. A. True B. False True Well pads commonly cover _____ acres. 3-6 Drilling practice that allows multiple wellbores to be drilled from a single, compact piece of land is known as Pad drilling. A. True B. False True A given well can drain a much smaller area in a shale well compared to conventional well. Low well spacing for shale wells is therefore necessary which often causes problems including __________________________. fracture interference (fracture hits) ________________ for shale wells is necessary which often causes problems including fracture interference (fracture hits). Low well spacing ____________________ are commonly developed using vertical wells to access multiple productive intervals over hundreds to thousands of feet Tight sand and carbonates Tight sand and carbonates are commonly developed using ___________ wells to access multiple productive intervals over hundreds to thousands of feet vertical When drilling in tight reservoirs, dense drilling may be required e.g. ________ wells per mile-square. 64 One important aspect in drilling shale wells is the need to drill the well lateral in a specific direction to maximize the chance of ________________________ in the reservoir. fracture propagation For deep reservoirs, the vertical stress is generally the ______ principal stress highest The stress in the subsurface can be characterized by ______ principal stresses perpendicular to one another. three The higher stress is referred to as the _____________ horizontal stress while the lower stress is the ____________ horizontal stress. maximum, minimum the ______ stress that needs to be exceeded in order to generate a fracture is the minimum horizontal stress. lowest the lowest stress that needs to be exceeded in order to generate a fracture is the ____________________________ minimum horizontal stress. The direction of least resistance along which the fracture would propagate is _________________ to the minimum horizontal stress. perpendicular The direction of least resistance along which the fracture would propagate is perpendicular to the ________________________ minimum horizontal stress. Therefore, identifying the direction of stresses is important and the well should be drilled in the direction of the _____________ horizontal stress. This enables fracture propagation _____________ to the well lateral direction minimum, perpendicular If the well is drilled in the direction of the maximum horizontal stress, the fractures would propagate along the well A. True B. False True If the well is drilled in the direction of the minimum horizontal stress, the fractures would propagate along the well A. True B. False False In deep shale reservoirs, fractures propagate in the direction of maximum horizontal stress. A. True B. False True A. ~3500 acres A fracture has 2 faces so when calculating surface area you should multiply the surface area by 2 How many perforation clusters on average make up each fracturing stage? 3-5 What will happen if the entire length of the well is perforated at once and fluids are injected without breaking it into stages? The majority of the well length will never get fractured Why do we frac in stages? Without stages fractures would only propagate at selective location where formation heterogeneities exist What are formation heterogeneities? Natural fractures or weaknesses induced by drilling In absence of heterogeneities, friction losses along the lateral cause the pressure to be highest toward the _________ which maximizes the chance of fracturing toward the ________ compared to _____ of the well. heel, heel, toe Friction losses along the lateral cause the pressure to be highest toward the toe which maximizes the chance of fracturing toward the toe compared to heel of the well. A. True B. False B. False The most common multistage hydraulic fracturing method is the _________________ method Plug-and-Perf (PNP) What is alternative to perforation when using PNP? Using cementable fracturing sleeves at the toe How do cementable fracturing sleeves work? When pumping pressure is applied, the sleeve opens and permits entry into the formation. If hydraulic fracturing job is conducted in a single stage, fractures will be most likely created near the heel. A. True B. False A. True Stages are labeled so that the first stage is at the heel and the last stage is at the toe. A. True B. False B. False Limited entry perforating enables evenly distributed stimulation fluid/energy across multiple perforation clusters within a stage. A. True B. False A. True Plug and perf multistage fracturing always requires coil tubing. A. True B. False B. False The number one reason that we use cluster perforations is ___________________________ Increase efficiency by decreasing operation time When fracturing a single well, the pumping crew and wireline crew can work in parallel and do not have to await the other. A. True B. False B. False If two or more wells are drilled, the available wireline crew can work on another well's perforation while the pumping crew are fracturing a given well. A. True B. False A. True Two or more wells are drilled which is a common practice in well pad drilling, the available wireline crew can work on another well's perforation while the pumping crew are fracturing a given well. This process is referred to as _________________ zipper fracturing What are two additional method of hydraulic fracturing completion? (Not PNP) - Ball-activated completion systems (BACS) - Coil Tubing Activation Completion System (CTACS) The neighboring wells are simultaneously fractured in zipper fracturing. A. True B. False B. False If the initial stage spacing is high, refracturing may be needed to fracture the inter-stage regions. A. True B. False A. True The fracture surface area may be lost during depletion due to: ____________________________ ____________________________ -stress increase - proppant loss/crushing/embedment/scaling Diverters can be used both during initial hydraulic fracturing as well as in refracturing. A. True B. False A. True Additives including gels and crosslinks are used to increase the _______________ of the fluid when pumped. viscosity "slickwater fracturing" is often used to refer to a _______ viscosity stimulation A. low B. high A. low "gel fracturing" is often used to refer to a _______ viscosity stimulation A. low B. high A. True Breakdown pressure is the pressure required to initiate and propagate the fracture. A. True B. False A. True The natural contrast in minimum horizontal stress between sand and shale helps containment of fracture within the sand. A. True B. False A. True Vertical stress is larger than minimum horizontal stress. A. True B. False B. False Critical depth is the depth at which maximum horizontal stress equals the vertical stress. A. True B. False A. True Vertical stress is larger than minimum horizontal stress at deeper intervals. A. True B. False A. True Fractures may initiate vertically but can turn horizontal when treatment pressure exceeds the overburden stress and from ______________ fractures T-shape T-shape fracture is undesirable since width of horizontal branch is very small. Proppant is unable to pass beyond the fracture wellbore interface and results in significant pressure loss and substantial fluid loss from the slurry. This describes a ________________________ Screenout Net pressure is uniform over the length of the fracture. A. True B. False A. True T-shape fracture is undesirable partly because it results in substantial fluid loss. A. True B. False A. True What are the three fracture geometry models used in petroleum engineering? -PKN when xf >> hf -KGF when xf << hf -Radial for approximately circular fracture When xf >> hf what fracture geometry model should we use? PKN When xf << hf what fracture geometry model should we use? KGD Which fracture geometry model is most relative to fracturing in ultra-low permeability formations? PKN Complex fracture geometries cannot be predicted using PKN, KGD, or Radial models A. True B. False A. True Doubling the fracture width requires multiplying the viscosity by a factor of A. 4 B. 1/4 C. 16 D. 1/16 C. 16 Which model is used when xf>>hf A. PKN B. KGD C. Radial A. PKN Based on PKN model, the hydraulic fracture will be long and narrow in a stiff rock. A. True B. False A. True Low contrast between horizontal stresses promotes complex fracturing. A. True B. False A. True Opening secondary fractures perpendicular to the main hydraulic fractures increases risk of screenout. A. True B. False A. True Activated natural fractures will not contribute to production unless propped. A. True B. False B. False ____________________ is a measure of a material tendency to expand in direction perpendicular to the direction of compression. Lower values are desirable. Poisson's ratio (v) ________________ is a measure of rock stiffness. Higher values are desirable. Young's modulus (E) ____________ values of Poisson's ratio are desirable for fracturing since it implies the rock is less stretchable. A. Higher B. Lower B. Lower Shale is _______________ if it is quartz rich or carbonate rich. brittle Shale is _____________ if it is clay rich ductile