Analysis of Geologic CO2 Migration Pathways in Farnsworth Field, NW Anadarko Basin

This study reports on analyses of natural, geologic CO2 migration paths in Farnsworth Oil Field, northern Texas, where CO2 was injected into the Pennsylvanian Morrow B reservoir as part of enhanced oil recovery and carbon sequestration efforts. We interpret 2D and 3D seismic reflection datasets of the study site, which is located on the western flank of the Anadarko basin, and compare our seismic interpretations with results from a tracer study. Petroleum system models are developed to understand the petroleum system and petroleum- and CO2-migration pathways. We find no evidence of seismically resolvable faults in Farnsworth Field, but interpret a karst structure, erosional structures, and incised valleys. These interpretations are compared with results of a Morrow B well-to-well tracer study that suggests that inter-well flow is up-dip or lateral. Southeastward fluid flow is inhibited by dip direction, thinning, and draping of the Morrow B reservoir over a deeper, eroded formation. Petroleum system models predict a deep basin-ward increase in temperature and maturation of the source rocks. In the northwestern Anadarko Basin, petroleum migration was generally up-dip with local exceptions; the Morrow B sandstone was likely charged by formations both below and overlying the reservoir rock. Based on this analysis, we conclude that CO2 escape in Farnsworth Field via geologic pathways such as tectonic faults is unlikely. Abandoned or aged wellbores remain a risk for CO2 escape from the reservoir formation and deserve further monitoring and research.

Stratigraphic variability of Mississippian Meramec chemofacies and petrophysical properties using Machine Learning and geostatistical modeling,STACK trend, Anadarko Basin, Oklahoma

Mississippian Meramec deposits and reservoirs in the Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher counties (STACK) play of central Oklahoma are comprised of silty limestones, calcareous sandstones, argillaceous-calcareous siltstones, argillaceous siltstones, and mudstones. We have used core-derived X-ray fluorescence (XRF) data and established environmental proxies to evaluate the occurrence of specific elements (Al, K, Ti, Zr, Sr, Ca, and Si) and to illustrate their stratigraphic variability. For the Mississippian Meramec, six indicator elements or element ratios serve as proxies for clay (Al and K), detrital sediment (Ti and Zr), carbonate deposits (Sr and Ca), calcite cement (Sr/Ca), and biogenic and continentally derived quartz (Si/Ti and Si/Al). We used an unsupervised K-means classification to cluster elemental data from which we interpret three chemofacies: (1) calcareous sandstone, (2) argillaceous-calcareous siltstone, and (3) detrital mudstone. We used a random forest approach to relate core-derived chemofacies to well logs and classify chemofacies in noncored wells with an accuracy of up to 83% based on blind test results. We integrated core-derived XRF, conventional well logs, and chemofacies logs to produce a dip-oriented cross-sectional chemofacies model that trends from the northwest to the southeast across the southern STACK trend. Meramec chemofacies distributions reflect parasequence stacking patterns. The stratigraphic variability of chemofacies indicates an upward increase of argillaceous detrital mudstone from parasequences 1 to 3. Parasequence 3 is capped by a maximum flooding surface. From parasequences 4 to 5, an increase in argillaceous-calcareous siltstone and calcareous sandstone reflects the progradational stacking. Porosity is relatively low in calcareous sandstones primarily due to calcite cement. Water saturation is high in argillaceous-calcareous siltstone, moderate in calcareous sandstone, and low in detrital mudstone. Within the Meramec, biogenic quartz is associated with drilling issues, specifically frequent bit trips due to its hardness. Interpreted biogenic quartz from element profiles corresponds to the calcareous sandstone chemofacies, which can be estimated from triple-combo well logs and can be mapped. Effective porosity and water saturation models reflect the stratigraphic variability of chemofacies and rock types and can be predicted within the defined chemostratigraphic framework. Understanding the spatial variability of effective porosity and water saturation is important for reservoir development planning.

Optimal Drawdown for Woodford and Mayes in the Anadarko Basin Using Data Analytics

Summary One of the enduring pieces of the jigsaw puzzle for all unconventional plays is drawdown (DD), a technique for attaining optimal return on investment. Assessment of the DD from producing wells in unconventional resources poses unique challenges to operators; among them the fact that many operators are reluctant to reveal the production, pressure, and completion data required. In addition to multiple factors, various completion and spacing parameters add to the complexity of the problem. This work aims to determine the optimum DD strategy. Several DD trials were implemented within the Anadarko Basin in combination with various completion strategies. Privately obtained production and completion data were analyzed and combined with well log analysis in conjunction with data analytics tools. A case study is presented that explores a new strategy for DD producing wells within the Anadarko Basin to optimize a return on investment. We use scatter-plot smoothing to develop a predictive relationship between DD and two dependent variables—estimated ultimate recovery (EUR) and initial production (IP) for 180 days of oil—and introduce a model that evaluates horizontal well production variables based on DD. Key data were estimated using reservoir and production variables. The data analytics suggested the optimal DD value of 53 psi/D for different reservoirs within the Anadarko Basin. This result may give professionals additional insight into more fully understanding the Anadarko Basin. Through these optimal ranges, we hope to gain a more complete understanding of the best way to DD wells when they are drilled simultaneously. Our discoveries and workflow within the Woodford and Mayes Formations may be applied to various plays and formations across the unconventional play spectrum. Optimal DD techniques in unconventional reservoirs could add billions of dollars in revenue to a company’s portfolio and dramatically increase the rate of return, as well as offer a new understanding of the respective producing reservoirs.

Mechanical stratigraphy of Mississippian strata using machine learning and seismic-based reservoir characterization and modeling, Anadarko Basin, Oklahoma

The STACK (Sooner Trend in the Anadarko [Basin] in Canadian and Kingfisher counties) play primarily produces oil and gas from Mississippian strata. The interval consists of interbedded argillaceous mudstones and calcareous siltstones. Such contrast in rock composition is linked directly to the mechanical stratigraphy of the strata. Brittle (calcareous siltstones) and ductile beds (argillaceous mudstones) are related to the sequence-stratigraphic framework at different scales. We use seismic and well log data to estimate and map geomechanical properties distribution and interpret the mechanical stratigraphy of rocks within the Mississippian strata. First, we defined the parasequences that form the main reservoir zones of the Meramecian-Mississippian strata. Once we established the stratigraphic framework, we estimated and compared rock brittleness index using two independent laboratory-based measurements from the core. The first method MIDBI (MIneralogical Derived Brittleness Index), uses mineralogical composition inverted from FTIR (Fourier Transform InfraRed spectroscopy) analyses, whereas the second method MEDBI (MEchanical Derived Brittleness Index), involves measurements of compressional and shear velocities from core plugs.We use the data from core-plug velocity measurements and well logs and an Artificial Neural Network (ANN) approach to establish relationships between geomechanical properties, well logs, and acoustic impedance values. We then applied these relationships to generate 3-D geomechanical models constrained to seismic volumes. The resulting grid distributions illustrate the stratigraphic variability of the properties at the parasequence scale. Overall, brittle strata decrease in thickness and abundance basinward as the frequency of interbedded brittle and ductile zones increases and gradually transitions into thin calcite-cemented siltstones and clay-rich mudstones. Analysis of the production performance of selected horizontal wells drilled within the Mississippian strata shows that the proportion of brittle and ductile rocks along the well path drilled and the drilled area vertical stacking pattern play a significant role in the hydrocarbon production for these Mississippian units.

Seismic illumination of small-offset seismogenic faults, Anadarko Basin, Oklahoma

In the past decade across the Central and Eastern U.S., there has been a substantial increase in the seismicity rate, which scientists broadly attribute to wastewater disposal and, to a lesser extent, hydraulic fracturing. Active clusters of seismicity illuminate linear fault segments within the crystalline basement that were unknown until seismicity began. Such surprises are due to the limited availability of 3D surface seismic surveys and the difficulty of imaging relatively shallow earthquake events from sparse seismic monitoring arrays. The Sooner Trend Anadarko Basin Canadian Kingfisher Counties (STACK) play of Central Oklahoma provides an opportunity to map such basement faults. Modern high-quality surface seismic data acquired to map the Meramec and Woodford unconventional resource plays enable us to image the basement faults and intrusions. Furthermore, because of increased earthquake risk from anthropogenic activities in the past decade, state regulatory agencies have deployed a relatively dense array of seismic monitoring stations, which allows us to integrate earthquake data into subsurface fault analysis. We have mapped structural deformation using a suite of seismic attributes, including multispectral coherence, volumetric curvature, and aberrancy, in a 3D seismic reflection data set covering 625 sq mi of the STACK area of the Anadarko Basin, Oklahoma. To unravel the relationship between the structures and seismicity, we use relocated locally recorded earthquakes and compute the focal mechanism solution for the relocated events. Our results reveal previously unmapped fault segments with dominant north–south, northwest, and northeast trends, most of which extend into the shallower sedimentary Hunton and Woodford Formations. Because of the small offset, we find that aberrancy and the curvature attribute best illuminate the basement-rooted faults in the study area. Fault segments with significant offset are better illuminated by band-limited multispectral coherence. We argue that the inherited structure of these faults makes them easily illuminable by flexure-related seismic attributes, especially within the sedimentary cover. The integration of the illuminated faults with relocated earthquakes and focal mechanism solutions shows that some of the illuminated faults that have hosted intrasedimentary and/or basement seismicity are reactivated strike-slip faults. We hypothesize that careful attribute mapping of faults and flexures, coupled with an understanding of the local stress and geomechanical properties, calibrated with recent seismic activity in the area, can help mitigate seismic hazards in tectonic settings where small-offset faults predominate.