Performance of Payoa Basal Eocene Block A Reservoir
- G.W. Clinton (Cities Service Oil Co.) | Jairo Ruiz (Colombia-Cities Service Petroleum Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 1968
- Document Type
- Journal Paper
- 31 - 35
- 1968. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 5.2.1 Phase Behavior and PVT Measurements, 1.6 Drilling Operations, 5.2 Reservoir Fluid Dynamics, 4.1.9 Tanks and storage systems, 2.4.3 Sand/Solids Control, 4.3.4 Scale, 4.6 Natural Gas, 5.1.2 Faults and Fracture Characterisation, 5.4.2 Gas Injection Methods, 4.1.5 Processing Equipment, 5.5.2 Core Analysis, 4.1.2 Separation and Treating, 4.2 Pipelines, Flowlines and Risers, 5.6.2 Core Analysis
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The Payoa field Eocene reservoir is a steeply dipping stratigraphic trap with a large vertical oil column overlain by a small gas cap. The trap for oil accumulation was formed by a major fault on the flank of an antidine, and cross-faulting divided the field into separate reservoirs. A 37" dip of the producing formations allowed 2,700 ft of oil column to exist between the initial gas-oil and water-oil contacts. The large vertical height of the oil column relative to the thin producing section created a variation in fluid characteristics from a saturated oil at the gas-oil contact to a highly undersaturated oil near the oil-water contact.
Modifications in theoretical methods of reservoir evaluation were necessary to predict reservoir performance because of the unique fluid and pressure characteristics. Fully realizing that an innovated approach to reservoir evaluation would be subject to considerable error, it was concluded that a gas injection and pressure maintenance program should be initiated early in the life of the field. Between the time the field was put on production and the initiation of gas injection, the reservoir suffered a decline in producing rate and a sharp decline in reservoir pressure. Also, the GOR increased quite rapidly. The pressure maintenance program has stabilized the producing rate and arrested the pressure decline. By shutting in the high GOR wells, the GOR was reduced and stabilized at a minimum. Estimates of reservoir performance show that the pressure maintenance program will recover 50 percent of the stock-tank barrels of oil in place as compared with only 15 percent recovery by primary depletion.
Payoa field, located approximately 200 airline miles north of Bogota, Colombia, in the middle Magdalena River valley, is operated by Cities Service Oil Co. for a combine consisting of Colombia-Cities Service Petroleum Corp., Pan American Colombia Oil Co., Colombia Atlantic Petroleum Co. and Empresa Colombiana de Petroleos. Each company recognized early that the Basal Eocene reservoir was a prime prospect for the application of reservoir engineering technology. An added incentive was the possibility of a large, irrevocable loss of oil if primary operations were conducted to their economic limit.
Often, in reservoir engineering perspective, neither the data nor the applicable calculation methods are completely adequate to describe reservoir performance. To some extent, previous experience must be utilized in conjunction with theoretical applications for each reservoir. In some instances, innovations to accepted theoretical calculations are necessary to describe reservoir performance.
A variation in reservoir fluid and pressure characteristics of the Basal Eocene reservoir presented a twofold engineering problem. First, fluid properties had to be developed that would effectively represent a variation from a saturated oil to a highly undersaturated oil. This data then had to be related to initial and saturation pressures so that a modified approach to the material balance and fractional flow concepts could be utilized to predict reservoir performance. This article presents the development of data and its application to reservoir performance estimates for the Basal Eocene reservoir labeled Block A in Fig. 1.
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