Tight Oil Reservoirs of the Midland Basin “Wolfberry”, Strawn, AND Mississippian

Reservoir Characterization and Production Properties

Currently, numerous oil and gas companies are directing their efforts toward the exploration and exploitation of “Tight Oil” from the Spraberry, Dean, Wolfcamp, Strawn and deeper Paleozoics in the Midland Basin. Production is co-mingled from these zones following multi-stage, hydraulic fracture stimulation of siltstones, carbonates and organic-rich mudstones spread out over a 2000 to 4000 foot depth range. Activity is centered in 10 counties in the Midland Basin and is spreading to adjacent areas.

These unconventional oil reservoirs have proved to be challenging in terms of 1) reservoir characterization, 2) identifying the many potential pay intervals that are interbedded in long intervals of indistinguishable shale, organic mudstone, siltstone and carbonate, 3) predicting producibility potential, 4) optimizing fracture stimulation techniques for maximum production, and 5) estimating ultimate recovery. Due to the thick section, many companies either do not have or have limited rock property data that are crucial for understanding these reservoirs. Therefore, in order to properly evaluate and exploit the thick section, appropriate types of rock property data need to be measured and integrated with log data, stimulation techniques, and production test information. These integrated data sets and case histories will provide operators with the critical parameters to optimize their exploitation and reduce finding and development costs.

The Integrated Reservoir Solutions Division of Core Laboratories is proposing to interested companies participation in a multi-company, geo-engineering, regional study of the prospective formations in the Midland Basin. This project consists of the characterization and evaluation of numerous conventional cores, rotary sidewall cores, and drill cutting samples taken from multiple wells targeting the zones of interest. Specifically, the prospective sections will be analyzed for geological, petrophysical, geomechanical, geochemical, and production properties. These data will be integrated with well logs, stimulation designs, and production test information. This large and searchable database will provide operators with valuable information not only on their own wells, but also on other operator’s wells. By sharing operator’s core data a more complete representation of the gross interval can be achieved.

The primary objective of this project is to provide operators with measured geological, petrophysical, geomechanical, geochemical, and production properties of the prospective formations in order to improve their formation evaluation and to optimize stimulation and production. Our work suggests that understanding the similarities and differences in the section on a regional basis is the key to successful exploration and exploitation. The resultant database will be an invaluable tool to operators in evaluating, comparing, and designing completion and stimulation methods. Specifically, the project objectives are as follows:

  • Geologically characterize the cored intervals in terms of depositional facies, environment of deposition, and rock types.
  • Characterize and classify the stratigraphic sections in terms of lithology, mineralogy, clay content, clay types, and pore structure including macro- and micro-fractures.
  • Measure the various petrophysical properties such as porosity, permeability, grain density, and saturations (i.e. water saturation, gas saturation, oil saturation, hydrocarbon filled porosity and bound water).
  • Measure and characterize the organic content of the mudstones in terms of total organic content (TOC), Rock Eval pyrolysis, and vitrinite reflectance.
  • Measure the key geomechanical properties that are required for optimizing fracture designs and/or horizontal wells such as Young’s Modulus, Poisson’s Ratio, Bulk Modulus, horizontal stress, and proppant embedment.
  • Determine rock-fluid compatibility and fracture conductivity of proppant and fluid-carrier systems in support of hydraulic fracture stimulation.
  • Core-log calibration of open-hole logs for the development of petrophysical models to determine potential “pay” zones for stimulation.
  • Integrate the core data with well logs, fracture stimulation techniques, and production test results to aid companies in their evaluation and exploitation of the reservoirs.
  • Provide a regional assessment of the various reservoir attributes to aid in exploration and exploitation.
  • Develop relationships from the database to aid in evaluating and comparing the various rock properties.
  • Provide operators with a searchable database for reservoir properties that can be used as analogs to aid in the appraisal and exploitation of new areas as the play expands