In -situ combustion (ISC) involves compression and injection of air into heavy/extraheavy oil reservoirs for enhancing production and recovery. Initially, ISC was very popular due to its high theoretical thermal efficiency, though more failures than successes in the 1990s made this process unpopular. It is a fact that it is now widely considered archaic. However, Suplacu de Barcau (Romania) and Balol-Santhal (India) ISC projects have brought the process back into focus. Performance of the Balol- Santhal-Bechraji over the last 25 years provides clarity to answer the question "Failure to enhance oil production and recovery by ISC: Myth or fact? " The author appreciates the views, decisions, and efforts of all global scientists/engineers/operators associated with the ISC process in the laboratory/field. Opinions and views presented in this paper are solely based on the author's experience, which may be in line or may differ. The discovery of heavy oil northwest of the Cambay Basin, India, in the 1970s led to the initiation of research and development in thermal processes. The depth, rock, and fluid characteristics, drive mechanism, and semi -arid area led to the testing of ISC over steam -flood in Balol. Laboratory findings are key to understanding the reaction kinetics of oil and process manifestations. Upgrading of oil is the key manifestation of ISC in the laboratory, but it is not seen in the field due to blending in long-distance displacement methodology. The involvement of laboratory personnel in design and surveillance plays an important role in the success of the project. Over the last 25 years, the Balol-Santhal ISC projects demonstrate the rejuvenation of declining fields with sustained enhanced oil production and an increase in recovery. Lessons of the Bechraji field indicate that process does not succeed in all reservoir settings. It is particularly suited to relatively clean, mobile heavy oil reservoirs with structural relief. Long-distance displacement of oil (vertical injector-vertical/horizontal producer spaced apart) is effective in a mobile oil reservoir. With low mobility oils, a short-distance oil displacement process using a pair of vertical injector and horizontal producer (horizontal well placed below the air injector) can be the preferred way for exploitation. This methodology has also the potential to capture upgraded oil. The process attracts more value when it is designed as operator friendly and flexible, integrating with gravity. Appropriate ignition types, continuous surveillance, maintaining optimum air injection rates, and re-engineering are important for the success of ISC. Success depends on the fabric and architecture of the reservoir, the way it is designed and implemented, and by integration of knowledge gained in the journey from laboratory to field with the process. It can be concluded that the perception of the ineffectiveness of ISC to enhance oil production and recovery from mobile heavy/extraheavy oil reservoirs cannot be generalized as a fact.
An underground stress state might be disturbed in an area, particularly adjusting to an active shear zone. Borehole breakouts (BOs) that appeared in a circular hole excavated in an inhomogeneous stress field might be tracked to identify the active shear zone. The present study aims to develop the breakout morphology analysis (BMA) algorithm to exploit the valuable attributes of borehole BOs including azimuth, width, and intensity (depth of elongation) of failure from wellbore ultrasonic imaging tools. In the current study, the extracted azimuthal information was surveyed to detect the active shear zone along the well. Ultrasonic data from five wells drilled in the doubly plunging Ahvaz Anticline located in Iran were collected for the purpose of algorithm verification. The multiwell correlation of the BOs' azimuth generated by the algorithm in the Ahvaz Anticline suggests a shear plan dipping southwest- northeast direction is possibly active in the deep vertical wells. Similarly, the seismic reflection profile of the Ahvaz Anticline shows a track of detachment faulting system in the mid- Cretaceous sediments. The finding confirms that the raw ultrasonic traveling time is more applicable than other borehole image data, such as static and dynamic images of ultrasonic amplitude, in BO characterization.
The significant quantities of oil contained in fractured karst reservoirs in Brazilian pre-salt fields adds new challenges to the development of upscaling procedures to reduce time on numerical simulations. This work aims to represent multiscale heterogeneities in reservoir simulators based on special connections between matrix, karst, and fracture mediums, both modeled in different grid domains within a single porosity flow model. The objective of this representation is a good balance between accuracy and simulation time. The principle combines the Embedded Discrete Karst Model (EDKM) and the Special Connection Fracture Model (SCFM), both developed by Correia et al, 2019. Therefore, this work extends the approach of special connections to integrate both karst and fracture mediums modeled in different grid domains and block scales. For a proper validation and numerical verification, we applied the methodology to a complex case study. The reference model is a refined grid model with: (1) an arrangement of large conduits (karsts), which are poorly connected, (2) a well-connected and orthogonal system of fractures and (3) a background medium (matrix). For the simulation model, the matrix grid domain has a grid block size of roughly 25 × 25 × 5 meters. The fracture domain has a grid block size of roughly 50 × 50 × 5 meters and the karst grid domain has the same block size as the reference model. Well-connected fractures are upscaled to the fracture domain by applying the Oda (1985) method. The results show a significant performance improvement regarding a dynamic matching response with the reference model, within a suitable simulation time and maintaining the dynamic resolution according to the representative elementary volume of heterogeneities, without using an unconstructed grid. Therefore, this work introduces a new method that can be applied to commercial flow simulators concerning the use of special connections to represent multiscale heterogeneities in flow simulators, without disregarding the accuracy over upscaling and an adequate simulation time.
Low primary and secondary recoveries of original oil in place from modern unconventional reservoirs begs for utilization of tertiary recovery techniques. Enhanced Oil Recovery (EOR) via cyclic gas injection ("huff ‘n puff") has indeed enhanced oil recovery in many fields and many of those projects have also been documented in industry technical papers/case studies. But the need remains to document new techniques in new reservoirs. This paper documents a small scale EOR pilot project in the eastern Eagle Ford and shows promising well results. In preparation for the pilot, full characterization of the oil and injection gas was done along with laboratory testing to identify the miscibility properties of the two fluids. Once the injection well facility design was completed a series of progressively larger gas volumes were injected followed by correspondingly longer production times. Fluids in the returning liquid and gas streams were monitored for compositional changes and the learnings from each cycle led to adjustments and facility changes to improve the next cycle. After completing five injection/withdrawal cycles in the pilot a few key observations can be made. The implementation of cyclic gas injection can be both a technical and a commercial success early in its life if reasonable cost controls are implemented and the scope is kept manageable. The process has proved to be both repeatable and predictable allowing for economic modeling to be utilized to help determine timing of subsequent injection cycles. A key component of the success of this pilot has been the availability of small compressors capable of the high pressures required for these projects and learning how to implement cost saving facility designs that still meet high safety standards.
Summary The emerging Paradox Oil Play in southeastern Utah is among the most significant unconventional plays in the western USA. The mean total undiscovered oil resources within just the Pennsylvanian Cane Creek interval of the Paradox Basin are believed to exceed 215 million barrels. However, to date, less than 5% (~9 million barrels) of the total Cane Creek resource has been produced from fewer than 40 wells, and only approximately one-half of those are horizontal wells. More than 95% of production is from the central Cane Creek Unit (CCU). Natural fractures are a key feature of many production wells, but stimulation by induced hydraulic fractures is not consistently successful. We hypothesize that more effective production in this play will rely on better fundamental characterization, especially on better quantification of the state of stress. Approximately 110 ft of core, well logs, and a diagnostic fracture injection test (DFIT) were acquired from the State 16-2 well within the CCU. With these data, we applied two methods to constrain and clarify the state of stress. The first technique, the Simpson’s coefficient method, provides lower bounds on the two horizontal principal stresses and relies on only limited data. Alternatively, the viscoelastic stress relaxation (VSR) method is used to estimate the least horizontal principal stress, building on observations that principal stresses become more isotropic as the viscous behavior of a rock is more pronounced. Results of these two methods support the hypothesis that the state of stress in the CCU of the Paradox Basin is nearly lithostatic and isotropic. Other factors consistent with this hypothesis include high formation pore pressure, which tends to reduce the possible stress states by changing the frictional failure equilibrium; lack of induced fractures in the core, which should be present in the case of stress anisotropy; and interbedded halite layers, which given their high degree of ductility, probably lead to greater VSR for the entire sedimentary package.
