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Abstract This paper presents the methodology and results of a reservoir characterization study of Clear Fork carbonates in the TXL South Unit Field located in Ector County, Texas. The principal objective of our study was to evaluate a targeted infill drilling strategy for future field development. Our study incorporated an integrated approach for which the primary evaluation tool was decline type curve analysis of well production data. The well performance analysis was both supplemented and complemented with petrophysical and geological studies, each representing different reservoir scales. On the basis of our study, we identified areas of the field with the highest reservoir quality and largest oil-in-place volume, thus identifying the areas of the field best suited for infill drilling. Introduction Like most Permian-age carbonate reservoirs in the Permian Basin, Clear Fork carbonates in the TXL South Unit Field are characterized by very thick, heterogeneous pay intervals with significant discontinuities, both laterally and vertically. Low reservoir energies, consistent with solution-gas-drive oil reservoirs, as well as low effective permeabilities to oil are manifested by primary production recovery efficiencies typically ranging from 8 to 12 percent on 40-acre well spacing. Consequently, infill drilling is required not only to increase recoveries from primary production, but also to enhance sweep efficiencies and improve recovery from secondary and tertiary enhanced oil recovery operations. Even at reduced well spacing, however, many operators observe low oil recoveries, poor sweep efficiencies, and early water breakthrough. Poor performance at a denser well spacing is indicative of the significant reservoir discontinuity. Accordingly, a better understanding of the reservoir heterogeneity will help to design and implement enhanced oil recovery operations more successfully. Moreover, operators in the Permian Basin have historically implemented "blanket" infill drilling strategies in which wells are drilled on uniform patterns and spacing with little consideration of reservoir quality. Development at non-optimum well spacing may result in poor economic returns, even under favorable oil pricing scenarios similar to current conditions. In fact, several previous studies have shown that "targeted" infill drilling programs are required to optimize field development by reducing capital expenditures and maximizing economic returns. Targeted infill drilling, however, requires a reservoir characterization program to identify areas of the field with the best quality rock and the largest volume of oil-in-place. Because of the significant volume of original oil-in-place remaining in Permian-age carbonates in West Texas, there is an economic incentive for optimizing field development with infill drilling programs, both for primary depletion and enhanced oil recovery operations. The purpose of this paper is to present the methodology and results of a reservoir characterization study of the Clear Fork carbonates in the TXL South Unit Field located in Ector County, Texas. Similar to a study conducted by Doublet, et al. for the North Robertson Unit in Gaines County, we incorporated an integrated approach in which we combined results from geological, petrophysical, and reservoir performance analyses, each representing different reservoir scales. Furthermore, rather than initiating a cost-prohibitive data acquisition program, we conducted our study using existing field data typically available to most operators. Historical Field Background Located in the center of the Central Basin Platform in the Permian Basin, the TXL South Unit encompasses approximately 10,200 acres in the western half of Ector County, Texas. Wells in the TXL South Unit produce from both the Upper Clear Fork (5600 Reservoir) and the Lower Clear Fork (Tubb Reservoir). As shown by Figure 1, current field production is about 1,000 STB/day and 3,000 Mscf/day from approximately 400 active wells.
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.96)
- Geology > Sedimentary Geology (0.68)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (31 more...)
An Integrated Geologic and Engineering Reservoir Characterization of the North Robertson (Clearfork) Unit: A Case Study, Part 1
Doublet, L.E. (Texas A&M U.) | Pande, P.K. (Fina Oil and Chemical Company) | Clark, M.B (Fina Oil and Chemical Company) | Nevans, J.W. (Fina Oil and Chemical Company) | Blasingame, T.A. (Texas A&M U.)
BRIEF SUMMARY Infill drilling of wells on a uniform spacing, without regard to reservoir performance and characterization, must become a process of the past. Such efforts do not optimize reservoir development as they fail to account for the complex nature of reservoir heterogeneities present in many low permeability carbonate reservoirs. These reservoirs are typically characterized by:โLarge, discontinuous pay intervals โVertical and lateral changes in reservoir properties โLow reservoir energy โHigh residual oil saturation โLow recovery efficiency The operational problems we encounter in these types of reservoirs include:โPoor or inadequate completions and stimulations โEarly water breakthrough โPoor reservoir sweep efficiency in contacting oil throughout the reservoir as well as in the near-well regions โChanneling of injected fluids due to preferential fracturing caused by excessive injection rates โLimited data availability and poor data quality Infill drilling operations only need target areas of the reservoir which will be economically successful. If the most productive areas of a reservoir can be accurately identified by combining the results of geologic, petrophysical, reservoir performance, and pressure transient analyses, then this "integrated" approach can be used to optimize reservoir performance during secondary and tertiary recovery operations without resorting to "blanket" infill drilling methods. New and emerging technologies such as cross-borehole tomography, geostatistical modeling, and rigorous decline type curve analysis can be used to quantify reservoir quality and the degree of interwell communication. These results can be used to develop a 3-D simulation model for prediction of infill locations. In this work, we will demonstrate the application of reservoir surveillance techniques to identify additional reservoir pay zones, and to monitor pressure and preferential fluid movement in the reservoir. These techniques are: long-term production and injection data analysis, pressure transient analysis, and advanced open and cased hole well log analysis. The major contribution of this paper is our summary of cost effective reservoir characterization and management tools that will be helpful to both independent and major operators for the optimal development of heterogeneous, low permeability carbonate reservoirs such as the North Robertson (Clearfork) Unit. Introduction There are many complicated factors that will affect the successful implementation of infill drilling programs in heterogeneous, low permeability carbonate reservoirs such as the Clearfork/Glorieta of west Texas. Before we began this project, we conducted an extensive literature review to gain a better understanding of the producibility problems we face at the North Robertson Unit (NRU). Fortunately, these reservoirs have a long producing history and there is a large quantity of useful data available from case studies for primary, secondary, and tertiary operations in the Clearfork and other analogous reservoirs. In a 1974 case study concerning waterflooding operations at the Denver (San Andres) Unit, Ghauri, et al gave valuable insights concerning reservoir discontinuity, injector-producer conformance, and the effect of reservoir quality on reservoir sweep efficiency. Poor reservoir rock quality and the existence of discontinuous pay between injection and producing wells resulted in a recommendation to reduce nominal well spacing from 40 acres to 20 acres. An outcrop study on the San Andres was performed to verify reservoir discontinuity. Injection wells were completed and stimulated preferentially in an effort to flood only the continuous layers of the reservoir. The original peripheral injection design was converted to inverted nine-spot patterns in an effort to decrease the amount of water channeling and early water breakthrough via the most permeable members. P. 465
- Overview (1.00)
- Research Report > New Finding (0.67)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.68)
- Geology > Sedimentary Geology > Depositional Environment > Transitional Environment > Tidal Flat Environment (0.68)
- Geology > Mineral (0.67)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (0.93)
- Geophysics > Seismic Surveying > Seismic Modeling (0.67)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.45)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (27 more...)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- (4 more...)
- Information Technology > Modeling & Simulation (0.87)
- Information Technology > Data Science > Data Quality (0.34)
Summary Data acquisition design and implementation challenges for mature reservoirs which are targets for Improved Oil Recovery (IOR) applications are discussed in this paper. Examples are provided for Shallow Shelf Carbonate (SSC) reservoirs in the Permian Basin of West Texas. What Are Mature reservoirs? Mature reservoirs are defined as properties with additional recovery potential by implementation of advanced reservoir characterization tools and techniques, reservoir management and/or changes in recovery mechanisms. Attributes of mature reservoirs are depicted in Figure 1, which shows the importance of reservoir characterization as a function of field development stage. Reservoir characterization and an understanding of heterogeneity become more important for maturing reservoirs as these factors have a profound impact on future reservoir development and management strategies. Mature reservoirs are typically characterized by some type of secondary drive mechanism. A change to a tertiary mode or implementation of other lOR methods may be necessary to extend the economic limit and productive life of the field. A team approach is also important to achieve data acquisition objectives in mature reservoirs. However, the data acquisition situation may be very different from that "new" reservoirs. The desire and need for IOR may be critical as the economic limit may be rapidly approaching and data required for IOR may not be available. Smaller reservoir size and lower remaining reserves may present economic constraints towards the acquisition of essential data for the implementation of many IOR methods. The lack of production, fluid properties and other data in the earlier stages of field development may present uncertainties in history matching with numerical simulation methods. This results in unreliable reservoir performance forecasts for IOR. Often, the implementation of data acquisition programs in mature reservoirs present opportunities to enhance near-term reservoir performance through effective reservoIr management. Data acquisition strategies for properties which are being considered for abandonment are not addressed in this paper. Redevelopment of these properties is often required to exploit behind pipe potential and undeveloped zones or horizons. INTRODUCTION - DATA ACQUISITION METHODOLOGY The data acquisition process for mature reservoirs can be segmented into two major areas:
- Geology > Sedimentary Geology > Depositional Environment (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (0.69)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.46)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (22 more...)