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Sometimes a new oil play is discovered by an explorer doing "the right thing for the wrong reason." That is how Ken Barbe, one of the founders and managers Manzano LLC, describes the decision to drill one of the first successful wells into a Permian play which is unconventional, but not in the way he and his partner had expected. The independent company drilled a horizontal well thinking "we were dealing with tight rock that produced limited amounts from vertical wells," he said. But when they fractured their first horizontal well they found more permeable rock producing a lot of water. That led to conversations with two other companies pioneering this zone that said it was to be expected.
Carbon dioxide (CO2) injected into oil fields is "the gift that keeps giving." The description comes from David Schechter, an associate professor of petroleum engineering at Texas A&M University, who is researching whether CO2 can be used to coax billions more barrels of oil from unconventional formations. In the United States, 318,000 B/D of oil production is credited to the injection of 3,443 billion ft3 of carbon dioxide. That estimate is based on a joint study by the US Department of Energy (DOE) and the University of Wyoming, which forecast that this technique for enhancing oil production could nearly double by 2018. That assumes a surge in the amount of CO2 captured from industrial sources to meet the growing demand.
Ren, Bo (The University of Texas at Austin) | Duncan, Ian (The University of Texas at Austin) | Male, Frank (The University of Texas at Austin) | Baqués, Vinyet (The University of Texas at Austin) | Lake, Larry (The University of Texas at Austin)
Brownfield residual oil zones (ROZ) may benefit from specific strategies to maximize production. We evaluated several strategies for producing from the Seminole ROZ. This ROZ lies below the main pay zone (MPZ) of the field. Such brownfield ROZs occur in the Permian Basin and elsewhere, formed by the action of regional aquifers over geologic time. CO2 can be injected into these zones to enhance oil recovery and carbon storage. Since brownfield ROZs are hydraulically connected to the MPZs, development sequences and schemes should influence oil production, CO2 storage, and net present value (NPV).
We conducted economic assessments of various CO2 injection/production schemes in the Seminole stacked ROZ-MPZ reservoir based on flow simulations. First, we constructed a high-resolution geocellular model from a seismic survey, wireline logs and core data. To calibrate the geological model and constrain the interface between the ROZ and the MPZ, we performed a comprehensive production-pressure history matching of primary depletion and secondary waterflooding. After this, we conducted flow simulations of water alternating gas (WAG) injection into the reservoir while considering several injection/productions schemes (e.g., switching injection from the MPZ to the ROZ, commingled production). For each scheme, various WAG ratios (i.e., reservoir volume ratio between injected water and CO2) were tested to find the maximum oil production and maximum CO2 storage. We assessed the economic results for each WAG ratio case on NPV.
The results from simulating various injection/production schemes showed that simultaneous CO2 injection into the MPZ and ROZ favors oil production. If instead, CO2 is injected into the MPZ and ROZ, then into the ROZ alone, this leads to increased CO2 storage. Storage performance is influenced by the interplay between the crossflow from the MPZ to ROZ and WAG ratios. As the WAG ratio increases, the amount of CO2 stored decreases more for commingled injection cases than for separated ROZ injection cases. Also, the WAG ratio leading to maximum oil production does not necessarily yield the largest NPV, because of the complicated interactions among CO2 consumption, reservoir heterogeneity, and oil recovery.
Brownfield ROZs are common below San Andres reservoirs in the Permian Basin, and they can be exploited to increase oilfields’ NPV and carbon storage potential. Our case study on the Seminole MPZ-ROZ is an analog for other similar reservoirs. We demonstrate that development sequences and WAG ratios influence the performance of CO2 EOR and storage. Thus, this work provides valuable insights into the further optimization of brownfield ROZ development and helps operators to plan flexible storage goals for stacked ROZ-MPZ reservoirs.
Ren, Bo (The University of Texas at Austin) | Male, Frank (The University of Texas at Austin) | Wang, Yanyong (The University of Texas at Austin) | Baqués, Vinyet (The University of Texas at Austin) | Duncan, Ian (The University of Texas at Austin) | Lake, Larry (The University of Texas at Austin)
Abstract The objectives of this work are to understand the characteristics of oil saturation in residual oil zones (ROZs) and to optimize water alternating gas (WAG) injection strategies. ROZs occur in the Permian Basin and elsewhere, and operators are using CO2 injection for enhanced oil recovery (EOR) in these zones. ROZs are thought to be formed by the flushing effect of regional aquifer flow acting over geological time. Both the magnitude of oil saturation and the spatial distribution of oil differ from water-flooded main pay zones (MPZs). We conducted flow simulations of CO2 injection into both synthetic and realistic geologic reservoirs to find the optimal injection strategies for several scenarios. These simulations of CO2 injection follow either man-made waterflooding or long-term natural waterflooding. We examined the effects of CO2 injection rates, well patterns, reservoir heterogeneity, and permeability anisotropy on optimal WAG ratios. Optimal is defined as being at minimal net CO2 utilization ratios or maximal oil production rates). Simulations of CO2 EOR show that the optimal WAG ratio for the ROZs is less than 1 (ratio of injected water and CO2 in reservoir volumes), and it depends, but in qualitatively different ways, upon the well pattern and reservoir heterogeneity. The optimal WAG ratio tends to increase with changing from inverted 9-spot (80-acres) to inverted 5-spot (40-acre) or increasing reservoir heterogeneity. The ratios for ROZs are consistently less than those observed in the same geologic models experiencing CO2 injection after traditional (man-made) waterflooding. This is because the water saturation caused by slow regional aquifer flow (~1ft/yr) differs from that created by traditional waterflooding. In ROZs, water prevails almost everywhere and thus it is less needed to ease CO2 channeling as compared to MPZs. This work demonstrates that optimal WAG ratios for oil production in ROZs are different from those in traditional MPZs because of oil saturation differences. Thus, commingled CO2 injection into both zones or directly copying WAG injection designs from MPZs to ROZs might not optimize production.
Dhote, Prashant Dhote (Kuwait Oil Company) | Al-Bahar, Mohammad (Kuwait Oil Company) | Cole, Anthony (DeGolyer and MacNaughton) | Al-Sane, Amal (Kuwait Oil Company) | Bora, Anup (Kuwait Oil Company) | Sreenivasan, Ashique (Kuwait Oil Company)
Abstract Residual Oil Zones (ROZs) are an area of incrasing attention from hydrocarbon E&P industry with ever depleting reserves in known oil accumulations and advent of Carbon Dioxide (CO2) Capture and Storage needs and technology. ROZ can serve as viable solution to both the future problems as a possible vast new oil resource and a prospect for reducing carbon emission. ROZs can be defined as thick pile of low-quality reservoir rock below traditional oil-water contact with about residual oil saturations of mainly irreducible oil resulting from the natural flushing of reservoir due to buoying forces and aquifer action in geological past in earlier oil-filled part of reservoir. The production of oil from ROZs from such reservoirs is technically and economicaly feasible through application of enhanced oil recovery techniques - largely through missible CO2 flooding/injection in the zone because of the nature of fluid and reservoir rock. The depostional and tectonic regime in the Kuwait Petroliferous Basins is investigated to demonstrate the occurrence of and independently assess ROZ potential. The understanding of Kuwait Petroliferous Basin indicates that ROZs might be developed by hydrodynamic actions associated with tectonic regime. The degradation of oil by water action and related increase of sulfur content of crude oil can be used as workable proxy for identification ROZ potential of the rerservoir. The regional mapping, understanding of tectionic history and regional systhesis of crude oil composition shows an extensive stratigraphic and lateral existence of ROZ potential across the Kuwait Petroliferous Basin. This study aims to provide strategic roadmap and detail data acquisition program that will reveal ROZ production potential in Kuwait for Kuwait Oil Company (KOC).
Abstract Residual oil zones (ROZs) are defined as those zones where oil is swept over geologic time period (natural flush) and exists at residual saturation. ROZs are increasingly being commercially exploited using CO2-enhanced oil recovery (EOR) (in Permian Basin). In this study, CO2 storage potential, long-term CO2 fate and oil recovery potential in ROZs are characterized. We use numerical simulations of CO2 injection with a reservoir model based on data from the Permian Basin. The changes of CO2 storage capacity and potential oil recovery with amount of CO2 injection are investigated. The effects of different well patterns (five-spot and line drive) and well spacing on fraction of CO2 retained in reservoir and cumulative oil production are also investigated. Furthermore, the effect of different CO2 injection modes, i.e., continuous CO2 injection and water-alternating-gas injection (WAG), on the CO2 storage and EOR potential are evaluated and compared. After the preliminary characterization of CO2 storage and EOR potential in ROZs, we next develop empirical models that can be used for estimating the CO2 storage capacity and oil production potential for different ROZs. A supervised machine learning algorithm, Multivariate Adaptive Regression Splines (MARS, (Jamali et al.)) is used for developing the empirical models. Results show that CO2 retention efficiency and oil recovery vary non-linearly with amount of CO2 injected. It is observed that long-term CO2 fate is a function of CO2 injection amount and significant fraction of reservoir CO2 resides in hydrocarbon phase. Five-spot well pattern results in more oil production and larger amount of CO2 retained in reservoir than line-drive well pattern. During the investigation of well spacing, we observe that less number of wells actually results in higher CO2 retention and oil recovery, and less number of wells can also result in less probability of wellbore leakage. In comparison of WAG and continuous CO2 injection modes, it is observed that WAG injection has higher fraction of injected CO2 retained in reservoir, but with slightly lower cumulative oil production. In the study of empirical models for the capacity assessment of CO2 storage and EOR, results show that MARS can generate high-fidelity empirical models that can be used to predict the cumulative CO2 storage capacity and cumulative oil production for different ROZs.
Abstract Recently, the miscible CO2-EOR tertiary process used in the main pay zone (MP) of suitable reservoirs has broadened to include exploitation of the underlying residual oil zone (ROZ) where a significant amount of oil may remain. The objective of this study is to identify the ROZ and to assess the remaining oil in a brownfield ROZ by using core data and conventional well logs with probabilistic and predictive methods. Core and log data from three wells located in the East Seminole Field in Gaines County, Texas, were used to identify the MP and ROZ in the San Andres Limestone, and to predict oil saturations. The core measurements were used to calculate probabilistic in-situ oil saturations within the MP and the ROZ as a function of depth. Well logs, in combination with core data and calculated saturations, on the other hand, were used to develop two expert systems using artificial neural networks (ANN); one to identify the ROZ and MP, and the other to predict oil saturation. These systems were also supported by a classification and regression tree (CART) analysis to delineate the rules that lead to classifications of zones. Results showed that expert systems developed and calibrated by combining core and well log data can identify MP and ROZ with a success score of more than 90%. Saturations within these zones can be predicted with a correlation coefficient of around 0.6 for testing and 0.8 for training data. The analyses showed that neutron porosity and density well log readings are the most influential ones to identify zones in this field and to predict oil saturations in the MP and ROZ. To explain the relationships of input data with the results, a rule-based system was also applied, which revealed the underlying petrophysical differences between MP and ROZ. This new predictive approach using machine learning techniques, could potentially address the challenges that previous studies have come up against in defining the ROZ within the formation and quantifying remaining oil saturations. The method can potentially be applied to additional fields and help reliably identify the ROZ and estimate saturations for future resource evaluations.
Alimahomed, Farhan (Schlumberger) | Haddad, Elia (Schlumberger) | Velez, Edgar (Schlumberger) | Foster, Randy (Triumph Exploration) | Downing, Terrell (Triumph Exploration) | Seth, Cody (Triumph Exploration) | Melzer, Steve (Melzer Consulting) | Downing, Will (Melzer Consulting)
Abstract The San Andres is one of the most prolific conventional carbonate plays in the Permian Basin. It primarily occurs in the Central Basin Platform, but some fields are spread throughout the Northwest Shelf. The variation of the log profiles across the platform indicates a staged history and, challenging geological setting, which can have an impact on the lateral variability, landing zones and the completion techniques. Horizontal wells being a relatively new way to exploit this play, there are several challenges associated with making it economic. These challenges were faced in a program involving three horizontal wells on the Central Basin Platform. High tier petrophysical and sonic logs in the pilot, sonic and image logs in the lateral, and real-time microseismic data, were analyzed in the program. Integrating data from various disciplines such as geology, petrophysics, geomechanics, completion engineering and reservoir engineering plays a significant role in identifying trends and key drivers of production. In the San Andres three-well program, high-tier petrophysical and sonic logging data were collected in the vertical pilot well. A fracture injection test (FIT) was performed to calibrate the rock properties. A 3D geomodel was built around the area of interest using well tops from offset vertical wells, and was refined to a localized structure around individual wellbores using dips from lateral image logs. Fracture simulations were performed to determine the optimum job size to cover the pay zone. Image logs in the lateral were interpreted for fractures and bedding planes, and to understand the changes in rock facies along the length of the lateral. Open hole sonic measurements in the lateral were used to place perforations in similar type of rock based on good reservoir quality and completion quality. Laboratory tests were performed on oil samples to determine the oil properties. Cuttings were analyzed to determine their solubility with acid. Two horizontal wells were monitored using real-time downhole microseismic. Post job analysis was performed to tie all the observations together. Analysis of the injection test indicated slightly lower than normal reservoir pressure. Pilot-hole logs indicated a variable zone with mobile oil (pay) which was overlain on the top by anhydrite stringers and beds; higher water saturations were observed below the zone. The three horizontal wells in this program were all landed at various depths from the mobile oil interval to understand the impact on production. Step down tests were performed and analyzed on several stages to quantify near-wellbore friction pressures. Microseismic data showed planar features in stages that had fewer fractures identified on the image logs. High treating pressures were observed on alternate stages indicating some degree of stress shadow. Image logs in the laterals showed features such as anhydrite nodules and distinct layering of the rock, which can have a significant impact on the hydraulic fracture growth and also on production. The analysis of the fracture treatment and microseismic data yielded important information, and the program included the adoption of appropriate technologies and formulation of workflows for effective analysis. The San Andres wells have been cost effective to drill and complete throughout the oil price downturn, but there are still many questions to be answered to make it an extremely successful play. The results and observations from this three-well program provide insights that will assist in planning and designing future projects.
This well pad for Manzano Energy serves two leases with about 8 wells. Most of the 16 tanks store produced water from wells producing about 15% oil, before it is sent via a company pipeline to its disposal well. "They were exactly right and we had firm in Midland, Texas, that is tracking thing for the wrong reason." That is how Ken Barbe, one of the the reservoir would work economically." Unlike wells in high-profile plays such founders and managers Manzano LLC, The three companies are among a as the Wolfcamp, oil production from describes the decision to drill one of the group of independents in West Texas that these wells declines more slowly so that first successful wells into a Permian play have shown it is possible to consistently "a year later it will be 100 to 150 B/D.