# Browsing by Subject "Unconventionals"

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Item Approximations in decision analysis and their applications to shale field development(2020-06-22) Beck, Andrew Alfred; Bickel, J. Eric; Hasenbein, John J.; Leibowicz, Benjamin D.; Pyrcz, Michael J.Show more Every decision analysis must strike a balance between cogency and verisimilitude. This is particularly challenging in the development of shale oil and gas assets, which are portfolios of options under price and production uncertainties. Decision makers maximize net present value by making periodic investment decisions, alternating between deciding which wells and infrastructure to invest in, and learning about the production and price environment. Current decision support tools are very simple, usually consisting of decision trees, fixed price decks, and no midstream constraints. Current optimization techniques are only applicable to very small, simplified problems. In this dissertation, we improve upon current techniques. We develop a heuristic that maps the current information of an asset, such as inventory, prices, and estimated production to a well schedule. The heuristic can be combined with optimization routines, decision trees, or strategy tables to improve decision quality and asset valuation. Next, we model a shale asset as a Markov Decision Process, allowing us to solve problems of a similar size and complexity to the state-of-the-art optimization techniques via dynamic programming. We compare the performance of the heuristic to the optimal solution on a set of small example problems, showing that its performance is comparable. Then we compare the performance of the heuristic to the decision tree method on a large example problem, showing that the heuristic performs significantly better. All decision makers are risk averse when the stakes get large enough. The literature gives general, qualitative recommendations about when to formally model risk aversion, but the recommendations are not specific enough. We develop a set of theoretical results on when an expected value analysis is sufficient, when an exponential utility analysis is sufficient, and when an analyst needs to use a non-CARA utility function that includes the decision maker’s entire portfolio. We use the Pearson distribution system and historical data from the S&P 500 to develop a representative set of alternatives over wealth that a decision maker might face in practice. We use our theoretical results to study our set of alternatives and derive a clear recommendation of when to use different utility models. We summarize our results in the “7-9-11” rule of thumb. If the alternatives in a decision problem are left-skewed, symmetric, or right-skewed, and the standard deviation of the returns is less than 7%, 9%, or 11% of the decision maker’s wealth, respectively, then an expected value analysis is sufficient, as formally modeling risk aversion will not have a material effect on the decisions. We also provide recommendations of when to move beyond an exponential utility function to a more accurate, non-CARA representation of utility, such as the linear-exponential utility function. Finally, we apply risk aversion to the shale asset management problem and explore the impact different risk tolerances have on decision making. We show that the more risk averse a decision maker is, the less she will invest. This suggests a certain minimum risk tolerance as a pre-requisite to investing in a shale asset. However, because individual decisions in shale are very small relative to the overall value of shale assets, introducing risk aversion has a limited effect overall on asset value.Show more Item Coupled geomechanics and compositional fluid flow modeling for unconventional oil and gas reservoirs(2019-02-14) Gala, Deepen Paresh; Sharma, Mukul M.; Bonnecaze, Roger T; Edgar, Thomas F; Mohanty, Kishore; Ribeiro, LionelShow more The integration of geomechanics with multi-phase, multi-component fluid flow in porous media has several applications in the upstream oil and gas industry. It can be applied for both near wellbore and reservoir scale problems in different reservoir types. The development of a 3D geomechanics and compositional flow model coupled with fracture growth capability is presented. The partial differential equations in the reservoir, fracture and well domain are solved in a coupled manner. The model is validated/verified for different physics such as fracture growth, stress around a fracture and well, phase behavior, multiphase flow, compressible flow and poroelasticity. The model is then applied to problems specific to low permeability shale and tight reservoirs, however, the model is very general and can be applied to any subsurface hydrocarbon or water reservoir. Propagation of multiple fractures using different fluids such as slickwater, gases and foams is studied using field scale examples. The impact of variables such as fluid compressibility, viscosity, wellbore volume, reservoir permeability, stress/tensile strength ratio, and poroelasticity on fracture geometry, breakdown and shut-in behavior is investigated in detail. Production from a well and the resulting stress changes are calculated in dry gas, gas condensates, black oil and volatile oil reservoirs. Permeability changes associated with an increase in effective stress on fractures and reservoir rock are shown to have a significant impact on decline rates. The impact of water evaporation and subsequent salt precipitation on productivity in shale gas reservoirs is evaluated. A sensitivity study is performed for variables such as capillary pressure, fracture spacing, reservoir permeability, initial brine saturation, reservoir temperature and well operating BHP. A method of fluid injection (water or gas) in depleted parent wells (known as pre-loading) to minimize damage due to frac-hits is studied. The stress and pressure changes due to fluid injection are shown to be dependent on injection fluid and reservoir fluid type, injection rates and the fracture geometry in parent wells. The compositional and geomechanical effects in a Huff-n-Puff gas injection IOR process in tight oil reservoirs are investigated. The additional recovery and increase in GOR after several Huff-n-Puff cycles is shown to be a function of reservoir and injected fluid composition and hysteresis in permeability as a function of effective stress.Show more Item Integrated stratigraphic and petrophysical analysis of the Wolfcamp at Delaware Basin, West Texas, USA(2022-04-12) Ramiro-Ramirez, Sebastian; Flemings, Peter Barry, 1960-; Bhandari, Athma R; Daigle, Hugh C; Kerans, Charles; Tisato, NicolaShow more Hydrocarbons stored in low-permeability reservoirs, also known as ‘unconventional reservoirs’, represent important energy resources worldwide. Although current technology allows their production at economic rates, there still are numerous production challenges and unknowns regarding their flow behavior. A better understanding on how fluids stored in these reservoirs are drained by the hydraulic fractures after stimulation may help to optimize completion designs and field development plans. This research is an attempt to describe such drainage behavior in the largest oil producing unconventional formation in the World. I investigated the drainage behavior in Wolfcamp reservoirs at the completion scale by integrating stratigraphic and petrophysical analyses with flow modeling. I interpreted the depositional and diagenetic processes that generated three Wolfcamp cores recovered in the central-eastern Delaware Basin, measured the porosity and permeability of distinct lithofacies, and developed simple models to describe flow in these strata. I found that most fluids (~95% of the pore volume) are stored in low-permeability (e.g., < 60 nD) mudstones that I interpreted as hemipelagics and siliciclastics turbidites. Interbedded with these deposits are the low-porosity (~5% of the pore volume) and low-permeability (e.g., < 50 nD) carbonate lithofacies that I interpreted as gravity flow deposits and diagenetic dolomudstones. The carbonate gravity flow deposits, when dolomitized, are up to 2000 times more permeable than the other deposits and represent preferential flow pathways that drain fluids from the low-permeability strata during production. This drainage behavior increases the reservoir upscaled permeability, and therefore production rates, multiple times higher compared to a reservoir consisting of only low-permeability strata. Hence, the presence of these permeable, dolomitized, gravity flow deposits plays a critical role when producing from Wolfcamp reservoirs as they accelerate drainage. These findings are also applicable to other low-permeability formations exhibiting significant permeability heterogeneityShow more Item Mechanistic and probabilistic rate-time analysis of unconventional reservoirs(2018-06-25) Ruiz Maraggi, Leopoldo Matías; Lake, Larry W.Show more Rate-time analysis is a widely used technique to forecast production in oil and gas production. The geological complexity of shale formations and their ultra-low permeability creates significant uncertainty on the behavior of these wells and their production forecast. This work is divided into two parts. The first, develops simple physics-based models to further understand the underlaying mechanisms of unconventional production. The second, introduces a probability approach that attempts to address the uncertainty in the production forecasts. The first part of this work presents mechanistic modeling of unconventional resources to estimate the ultimate recovery (EUR), drainage volumes and recovery factors of wells. Using dimensional analysis, we cast the dimensionless groups of the one-dimensional compressible and slightly compressible single-phase and single porosity diffusivity equation (constant well pressure case). The solutions present the driving force for oil and gas production (drainage mechanism) and its parameters as two desired physical quantities: stimulated volume and characteristic time. Furthermore, we show that this equation is general for the three-dimensional case when there are no-flow boundaries in the other directions. Using this approach, we introduce a rigorous solution for two-phase flow of the slightly compressible diffusivity equation. Moreover, we propose an approximate solution of the single-phase and double-porosity cases of the slightly compressible diffusivity equation. In addition, we develop a modification of the Unconventional CRM equation reducing its parameters to the ones present in the solution of the diffusivity equation. Finally, we present application examples of the discussed models to wells from the Bakken/Three Forks, Wolfcamp/Spraberry and Haynesville Formations. The second part of this thesis displays the application of a probability approach to forecast the production of unconventional wells. The procedure involves sampling the production data, then matching these realizations with different rate-time relations to get EUR distributions for each model. Finally, the method assesses the performance of each rate-time relation with a probability to output a weighted EUR distribution for a given well. A weighted EUR distribution comes closer to acknowledging the uncertainty present in the production forecast. Finally, the procedure is applied to forecast production of wells of the Bakken, Wolfcamp and Haynesville Formations.Show more