Abstract

Microbiologically enhanced oil recovery (MEOR) is the use of microorganisms to facilitate, increase or extend oil production from a natural reservoir. The concept is more than 40 years old, however, early proposals were poorly conceived and in most instances of no practical value. Recent studies have developed microbial biotechnology to resolve specific production problems such as pressure depletion and sweep inefficiency in a target reservoir.

Field trials to determine and document the effectiveness of microbial process, and to assess the validity of laboratory studies and models have been conducted. The application of MEOR in these trials has resulted in a substantial and sustained increase in production compared to control operations on the same reservoir. Increased production has been sustained from a single treatment.

A field assessment of the new technology in the Alton field is described. Twelve months after treatment an approximate 40% increase in net oil production continues. The test is unique because production continues. The test is unique because of the stringent controls applied during the assessment.

Introduction
Alton Field

The Alton Field is located 370 km (230 miles) west-southwest of Brisbane in the Surat Basin, Queensland, Australia. The Alton Field produces from Lower Jurassic, Boxvale Sandstone which is part of the Evergreen formation. The trap is structural-stratigraphic; small anticlinal closure with.

reservoir zones controlled by permeability barriers and edge-water contacts. The reservoir temperature is 76 deg. C (169 deg.F). Production commenced in January 1966 and at present the field is producing on beam pump from five wells. producing on beam pump from five wells. The individual sands in Alton tend to be thin with a permeability of 11 to 884 md (average 260 md) and porosity of 15.4 to 19.8% (average 17.2%). The porosity of 15.4 to 19.8% (average 17.2%). The permeability and porosity decrease from east to permeability and porosity decrease from east to west. The hydrocarbon areal extent is 1840 acres. The original oil in place has been estimated at between 6.6 million STB and 13.6 million STB. Oil produced is medium light on a paraffin base. produced is medium light on a paraffin base. Residual oil concentration is about 50%. The pressure and production history indicates the pressure and production history indicates the presence of a weak water drive which is presence of a weak water drive which is supplemented by fluid expansion.

The Alton Reservoir commenced production at a rate of 1000 STB/day. Field Production started a slow decline in 1969 and there has been a roughly exponential deline since. In recent years that decline has been measured at approximately 15 percent per annum and the reservoir is close to its percent per annum and the reservoir is close to its economic limit of 15 STB/day.

The low primary recovery and high residual oil saturation make Alton a prime candidate for enhanced oil recovery. After initial evaluation it was considered that a waterflood would be too expensive and the stratified nature of the sands at Alton were considered to militate against its likely success.

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