Fireflooding a High-Gravity Crude in a Watered-Out West Texas Sandstone
Authors: Anthony Mark J. , Taylor Tim D. , Gallagher Bill J. 
Published: December 2007

This paper describes the results, operational problems encountered, and the ongoing technical evaluation of an in-situ combustion pilot project in the North Ward-Estes field in Ward County, TX (Fig. 1). This sandstone reservoir was discovered in 1929 and has been under waterflood since 1955. Even though the reservoir characteristics were marginal in comparison with the screening criteria for in-situ combustion, laboratory tests indicated that this process could be viable.

Introduction

The North Ward-Estes field is an anticlinal structure of lagoonal deposition 18 miles (28.9 km) long and 4 miles (6.4 km) wide, trending north to south along the western edge of the central basin platform. The Yates formation is located at a depth of 2,400 to 2,800 ft (732 to 853 m). This Permian age reservoir consists of seven sand members trapped by dense dolomites and is limited a really by shales and evaporites. Approximately 10% of the rock volume consists of clay: montmorillonite, 80 to 85%; illite, 5 to 10%; chlorite, 1 to 5%. Some minor evidence of fracturing has been indicated, and a northwest-southeast directional permeability is also present.

The G.W. O'Brien Well 4 was drilled in April 1929 by Gulf Oil Exploration and Production Co. After this discovery well, approximately 2,000 wells producing from the Yates and Queen formations were drilled over an area of about 30,000 acres (121 × 10(6) m2). By 1955 most of the primary oil was depleted by solution gas drive. At that time, a waterflood was initiated that still remains in operation. Production and injection have been from open hole multi sand completions, which do not lend themselves to reliable calculations of oil saturation. Approximately 350 million bbl (55 × 10(6) m3) of oil have been produced from this reservoir since discovery.

A dry forward in-situ combustion pilot was initiated on April 11, 1978. This project, known as the Section 10 combustion project, was implemented in the J-2 sand, which is the lowest of seven Yates sand members (Fig. 2). The rock and fluid properties are given in Table 1. Comparison of project parameters with various screening criteria indicated that the reservoir oil saturation was marginal (Table 2). All other parameters were within the minimum criteria. Laboratory experiments using produced fluids and preserved core demonstrated the applicability of an in-situ combustion process in this watered-out reservoir. We initiated a pilot project to substantiate these tests and to answer four major objectives:Can ignition be obtained and can combustion be propagated in a light-gravity crude?Can flue gas be isolated from other producing sands?Can produced flue gas be disposed of readily?Will the oil-production rate be increased?

This pilot was implemented in two phases. We conducted Phase 1 in an inverted 10-acre (40 469-m2) five- spot pattern. High O2 and low CO2 concentrations in gas samples from offset producing wells indicated marginal bum quality. Rapid flue gas migration and the evidence of a low-quality bum caused this phase to be terminated in April 1979.

In Nov. 1978, we began Phase 2 in an inverted 40-acre (161 875-m2) nine-spot pattern west of the Phase 1 pilot in a location having a thicker sand section. The initial O2 and CO2 concentrations in the produced flue gas indicated a better burn quality in this area. An observation well was dulled and cored behind the calculated location of the combustion zone to determine whether ignition was obtained and whether combustion propagation was possible in this formation. Another observation well was drilled and cored in an attempt to locate the leading edge of the combustion zone and to determine whether an oil bank was developing.

JPT

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