Old Field - New Life

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 94669, "New Life to an Old Field," by J.S. Swanson, SPE, and D.C. Swanson, SPE, Grail Quest Corp.; M. Jarvis, Penn Virginia Oil & Gas Corp.; and R. Hall, SPE, Grail Quest Corp., prepared for the 2005 SPE Hydrocarbon Economics and Evaluation Symposium, Dallas, 3-5 April. The East Tunstill field is a tight, undersaturated sandstone reservoir with a 9% recovery factor on primary depletion. Marginal production and a previous relatively unsuccessful waterflood did not show the potential value of the field. A detailed analysis revived the field. Challenge To increase the value of this field, within a limited budget, new procedures and methods were necessary. A project workflow had to be designed to analyze the field characteristics, taking into account the high number of wells and many years of production, which provided a large amount of useful data. The operator believed that an improved reservoir description applied with simulation methods could yield a better understanding of reservoir drainage, fluid movement, and the volume and location of the remaining oil. Additionally, the operator decided to use a volumetric-balancing technology that enabled quick analysis of various waterflood injection/producer patterns to determine the most economical and efficient flood pattern and, thereby, demonstrated the field's potential. Background The East Tunstill field is in the Delaware basin in Loving County, Texas. Discovered in 1959, cumulative production is estimated at 2.9 million bbl of oil, 8.2 Bcf of gas, and 5.8 million bbl of water. The field produces from the Delaware Olds formation, in the upper Bell Canyon sand series. An improved reservoir-description study with reservoir parameters yielded estimated original oil in place (OOIP) of 30 million bbl. Project Workflow and Methodology The operator initiated the project with two main goals as follows.Confirm existence and volume of remaining recoverable oil and its location.Design a development plan for the most efficient maximum economical oil recovery. Data Preparation The first major step in the workflow was the geologic study, including a detailed stratigraphic analysis as well as a review of the depositional facies on the basis of field-core information. The knowledge of the facies supported the biased mapping of the reservoir, which then determined the controlling characteristics and flow paths of the reservoir fluid. To complete the static reservoir description, basic reservoir parameters were applied to calculate the OOIP. Dynamic Analysis Once the OOIP was determined, the process determines how fluids were drained or produced over time. The fluid movement (involving both production and injection) was tracked in the reservoir over the life of the field by use of volumetric balancing. This method uses the following data sources.Base map with well locations and completion information.Net sand/facies map depicting the remaining reserves recovery.Original-hydrocarbon-in-place maps.Well-production history.Well-injection history.