Formation Analysis and Reservoir Performance StudyTensleep Reservoir, Hamilton Dome Field
- J.K. Thompson (Arco Oil and Gas Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1981
- Document Type
- Journal Paper
- 245 - 253
- 1981. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 5.6.1 Open hole/cased hole log analysis, 4.1.2 Separation and Treating, 1.2.3 Rock properties, 1.6 Drilling Operations, 5.2 Reservoir Fluid Dynamics, 5.1.2 Faults and Fracture Characterisation, 2.2.2 Perforating, 3 Production and Well Operations, 5.5.2 Core Analysis, 3.1 Artificial Lift Systems, 5.1.1 Exploration, Development, Structural Geology, 4.1.5 Processing Equipment, 3.1.1 Beam and related pumping techniques, 5.2.1 Phase Behavior and PVT Measurements, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.1 Reservoir Characterisation, 5.7.2 Recovery Factors
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A joint geologic/engineering study of the Tensleep reservoir in the Hamilton Dome field in Wyoming was undertaken (1) to define reservoir characteristics, (2) to evaluate fully the reservoir's primary performance, and (3) to recommend operation and exploitation procedures to maximize oil recovery efficiency. An improved understanding of reservoir zonation, natural formation fracturing, and water influx behavior resulted in a development drilling program on several leases that significantly increased oil production rate and ultimate oil recovery. Prediction methods also were developed to project future water influx volumes and probable water/oil ratio (WOR)trends.
The Hamilton Dome field is on the southwest side of the Big Horn basin in northwest Wyoming (Fig, 1). Production has been obtained from six geologic strata ranging in depth from 1,500 to 3,500 ft (457 to 1067 m) over a productive surface area of 2,500 acres (10 x 10(6) m). The structure, discovered in 1918, had 500 million bbl (79 x 10(6) m3) of original oil in place (OOIP) in the six producing formations and has produced at rates of more than 25,000 BOPD (3975 m3/d oil).
This paper principally deals with the major pay horizon in the field- the Pennsylvanian Tensleep reservoir - which had an OOIP volume of 375 million bbl (60 x 10(6) m3). The Tensleep reservoir produces 20 degrees API (0.93-g/cm3), 42-cp (0.042-Pas) crude from an average depth of 2,750 ft (838 m). Cumulative oil production totals 147 million bbl (23 x 10(6)m3) of oil with producing energy in this highly undersaturated reservoir supplied by a very active water drive. Basic rock and fluid properties are summarized in Table 1 and are averages; actual fluid properties vary significantly with structure as discussed in a later section.
The Tensleep formation, which averages 200 ft (61 m) in net pay thickness, was considered, in previous reservoir studies, a relatively uniform, massive sandstone overlying an occasionally productive basal dolomitic section. However, more recent well logs from a few wells in the late 1960's and mid-1970's indicated a more complex zonation. Selective testing in some of the same wells showed higher pressures and more economic water cuts in certain lower Tensleep intervals, indicative of poor drainage.
Also, water encroachment in the field was extremely erratic. Numerous wells in the center of the field had experienced water breakthrough and reached noneconomic water cuts, while wells located on the structure both downdip and updip of the central region were water-free or at low WOR's. A joint geologic/engineering study of the Tensleep reservoir was undertaken(1) to define reservoir characteristics, (2) to evaluate fully the reservoir's primary performance, and (3) to recommend future operation and exploitation procedures for maximizing oil recovery efficiency.
An improved understanding of the Tensleep's complex reservoir zonation led to an infill drilling program, which significantly increased oil rate and ultimate recovery. Shut-in of high water cut producers in certain problem areas further boosted oil production. A concurrent analysis of infill drilling results and the water influx behavior as influenced by natural formation fracturing has helped to explain the unusual water encroachment pattern in the field. The fracture study discussed in this paper applies previous laboratory and geology field work to illustrate natural fracture geometry on folded structures. Prediction methods also were developed to project future water influx volumes and probable WOR trends.
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