West Waha and Worsham-Bayer fields are located in the Southeastern Delaware Basin, West Texas. For several decades, these fields have been experiencing problem of low natural gas recovery in contrast to their large estimated reserves. This study involved the integration of interpreted three data sets namely; 10 well logs, 20-sq- miles 3D seismic and production data. The principal objectives for this study were to determine the impact of thin-beds on reservoir petrophysical analysis and to assess the impact of estimated recoverable reserve on the interpreted reservoirs (R1 [Lower Ordovician Ellenburger group], R2 [Silurian Fusselman formation], R3 [Devonian Thirtyone Formation] and R4 [Undifferentiated Mississippian Limestone].
Reservoir characterization method employed were: well log correlation, petrophysical analysis to calculate porosity and Movable Hydrocarbon Index (MHI), reservoir attribute analysis for thickness estimation, seismic-to- well ties to detect the reservoirs of interest, fault mapping, 3D seismic interpretation, generation of time-depth structure maps for prospect mapping, volumetric analysis for recoverable reserve estimation and production record interpretation.
Well log correlation revealed complex thrust faulting, structural rotation and left- lateral strike-slip which serves as major traps in some areas of the fields. The reservoirs were thickening to Northeastern direction towards Texas arch and thinning Northwestern and the log motifs depict carbonate depositional environment type. The mean porosities for R1, R2, R3 and R4 reservoirs are 23.7%, 16.3%, 26.1% and 26.0% respectively, while the fields' mean porosity value is 23.1% showing excellent porosity value for natural gas flow. Wells 29, 36, 37 and 38 have MHI of >20%. R1 reservoir had the highest thickness value (146 ft) at well log 29. F1 and F2 are major faults and F3, F4, F5, F6, F7 and F8 and F9 are minor faults. F3, F2, F4, F5, F6, F7 and F8 dip north, while F1, F3 and F9 dip south. The total Gas in place (BScf) and the total Recoverable reserve (Tcf) calculated were 359.73 and 636.62 respectively. Production records interpretation showed decrease in reservoirs' productivity as a result of decline in the natural pressure of the reservoirs. From analysis results, it was deducted that the thin beds positively impact the reservoir petrophysics and the calculated recoverable reserve also impact reserve.
Table of Contents
1.0 Introduction
1.1 General Statement
1.2 Study Location
1.3 Statement of the problem
1.4 Objectives of study
1.5 Physiographic Setting
1.5.1 Topography
1.5.2 Climate
1.6 Scope and Methodology
1.7 Previous work
2.0 Regional Geology of Texas
2.1 Generalized Geology of Texas
2.1.1 Geology of West Texas
2.2 Geologic history of West Texas
2.3 Regional Geology of Delaware Basin
2.3.1 General Statement
2.3.2 Geology of Delaware Basin
2.4 Geologic Setting of West Waha and Worsham-Bayer Fields
2.4.1 Ellenburger Group Reservoir Geology
2.4.1.1 Ellenburger Group Depositional Facies Assemblages
2.4.1.2 Karst Facies of Ellenburger Group
2.4.2 Fusselman Formation Reservoir Geology
2.4.3 Thirtyone Formation Reservoir Geology
2.4.4 Undifferentiated Mississippian Reservoir Geology
3.0 Methodology
3.1 Data Volumes
3.2 Use of the Data
3.3 Summary of the Data
3.4 Place of Data Interpretation
3.5 Procedure for Interpretation
3.5.1 Well log correlation
3.5.2 Calculation of Petrophysical parameters
3.5.3 Reservoir attributes
3.6 Seismic-to-well ties
3.7 3D Seismic Interpretation
3.7.1 Mapping of reservoirs
3.8 Structural Framework/Fault Network Mapping
3.9 Time-Depth Structure maps (Depth Conversion)
3.10 Recoverable reserve estimation/Volumetric
3.11 Production record interpretation
3.12 Limitation of study
4.0 Results and Discussion
4.1 Well log correlation
4.1.1 Petrophysical analysis
4.1.2 Reservoir Attribute Analysis Result
4.2 Seismic-to-well ties using check survey
4.3 Structural Framework/Fault Network Mapping
4.4 3-D Seismic Mapping
4.5 Time-Depth Structure Maps
4.6 Recoverable reserve estimation/volumetric result
4.7 Production record interpretation
5.0 Conclusion and Recommendation
Research Objectives and Key Topics
The primary objective of this research is to perform a detailed reservoir characterization of the West Waha and Worsham-Bayer fields in the Southeastern Delaware Basin, West Texas, to address the issue of low natural gas recovery despite significant estimated reserves. The study investigates the petrophysical characteristics of key reservoirs and the structural complexity of the basin to enhance future production efficiency.
- Integration of well logs, 3D seismic data, and production records for detailed reservoir characterization.
- Petrophysical analysis focusing on porosity, Movable Hydrocarbon Index (MHI), and reservoir thickness.
- Structural and fault network mapping to understand trapping mechanisms in the Delaware Basin.
- Volumetric analysis and estimation of recoverable natural gas reserves.
- Evaluation of reservoir compartmentalization and its impact on gas production performance.
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1.1 General Statement
Reservoir characterization and subsurface geological maps is perhaps the most important vehicle used to explore for undiscovered hydrocarbons and to develop proven hydrocarbon reserves. However, the subject of reservoir characterization and subsurface mapping is probably the least discussed, yet most important, aspect of petroleum exploration and development. As a field is developed from its initial discovery, a large volume of well logs, seismic, and production data are obtained. With the integration of these data, the accuracy of the subsurface interpretation is improved through time (Tearpock and Biscke, 2003).
A decade ago, approximately 800 trillion cubic feet (Tcf) of natural gas existed or was estimated to exist in conventional reservoirs in United States, yet only 538 Tcf of this gas is economically recoverable at prices of less than $3 per thousand cubic feet (Mcf) in 1987 dollars (Finley et al., 1988). More recently, considering only the largest 580 gas reservoirs on Texas State Lands, only half of an original 20 Tcf of natural gas in place has been recovered (Holtz and Garrett, 1997). One of the most promising new technologies for imaging gas reservoirs for reserve-growth studies is three-dimensional (3-D) seismic reflection data. The recent rapid increase in the use of 3-D seismic data in the oil and gas industry has vastly improved the level of detailed resolution of subsurface reservoir parameters such as petrophysical features (porosity, permeability, water saturation and so on), structural features interpretation (faults and folds), stratigraphic features (erosion and truncation features, karsting etc), and in some cases, even direct hydrocarbon indicators (so-called "bright spots"). The data set used was acquired in the West Waha and Worsham-Bayer fields area of the southeastern Delaware Basin, West Texas (Fig. 1.1), comprising of three categories : (1) approximately 20 square miles (51.8 Km2) of 3-D seismic data, (2) well data, including digitized well logs from 11 wells within the 3-D seismic data volume, and a check-shot survey for well 37, and (3) production record from the wells.
Summary of Chapters
1.0 Introduction: This chapter outlines the problem of low natural gas recovery in the West Waha and Worsham-Bayer fields and establishes the study's objectives, which include petrophysical analysis and reserve estimation using integrated datasets.
CHAPTER TWO: Provides a comprehensive overview of the regional geology of Texas and the Delaware Basin, detailing the stratigraphic and structural history relevant to the reservoirs.
CHAPTER THREE: Describes the methodology, including the integration of seismic data, well logs, and production records to perform petrophysical analysis, fault mapping, and volumetric calculations.
CHAPTER FOUR: Presents the results of the well log correlation, seismic interpretation, and reserve estimation, discussing the impacts of structural features and petrophysical properties on gas production.
CHAPTER FIVE: Concludes the study by summarizing the findings regarding gas productivity and providing recommendations, such as mechanical fracturing and secondary drilling, to improve recovery efficiency.
Keywords
Reservoir Characterization, Delaware Basin, West Texas, Ellenburger Group, Fusselman Formation, Thirtyone Formation, Mississippian Limestone, 3D Seismic, Petrophysical Analysis, Well Log Correlation, Natural Gas Recovery, Fault Mapping, Volumetric Estimation, Porosity, Reservoir Compartmentalization.
Frequently Asked Questions
What is the primary focus of this research?
This research focuses on performing a comprehensive reservoir characterization of the West Waha and Worsham-Bayer fields to identify why these fields suffer from low natural gas recovery despite having large estimated reserves.
What datasets were integrated for this study?
The study integrates interpreted data from 10 well logs, approximately 20 square miles of 3D seismic data, and historical production records from the wells.
What is the main goal of the study?
The principal objective is to determine the impact of thin-beds on petrophysical analysis and to assess the recoverable natural gas reserves of the four main interpreted reservoirs (R1, R2, R3, and R4).
Which scientific methods were employed?
The methodology includes well log correlation, petrophysical analysis (porosity and MHI calculation), 3D seismic interpretation, structural fault network mapping, and volumetric analysis for reserve estimation.
What does the main body of the work cover?
The main body covers the regional geology of the Delaware Basin, detailed methodology for subsurface analysis, the presentation and discussion of results, and final conclusions with recommendations for future operations.
Which keywords define the core of this work?
Key terms include reservoir characterization, Delaware Basin, 3D seismic interpretation, petrophysical analysis, gas reserve estimation, and structural mapping.
Which reservoir is identified as the major producing unit?
The Lower Ordovician Ellenburger Group (R1) is identified as the major gas-producing unit in the studied fields.
What specific structural features were identified as traps?
The study identified complex thrust faulting, structural rotation, and left-lateral strike-slip as the major structural traps serving the fields.
How do thin beds influence the reservoir performance?
The analysis indicates that thin beds (by-pass beds) positively impact the reservoir petrophysics and the calculated recoverable reserves.
What are the key recommendations for increasing production?
The author recommends mechanical fracturing to address compartmentalization, artificial pressure maintenance via fluid injection, and secondary redrilling of wells currently sited in suboptimal locations.
- Quote paper
- Emelda Orakwue (Author), 2010, Reservior characterization of West Waha and Worsham-Bayer Fields, Munich, GRIN Verlag, https://www.grin.com/document/215030
