New Life for a Mature Reservoir Through the Judicious Application of Technology - Arab D, Dukhan Field, Qatar

Abstract

A judicious mixture of "old/classical" and "new" technology has created the opportunity for new life for the mature Arab D reservoir, Dukhan Field. Classical technology has identified large dormant oil reserves in attic situations, and under the gas cap. Exploitation of this "new" oil is being done with the use of horizontal drilling technology. Introduction "Cutting edge" technology is viewed by many in our industry today as a panacea, whereas "old/classical" technology has become for them irrelevant. This paper has three objectives:to document a paradigm from Qatar disproving this fallacy.to show how a judicious mix of old and new technology has provided new life for a mature reservoir.to highlight the importance of understanding the history of a mature reservoir, before embarking on the search for new oil within it. The Arab D Reservoir, Dukhan Field1,2 The giant Dukhan Field is located onshore, western Qatar, and is roughly 44 miles (70 km) long (fig. 1). There are three oil bearing reservoirs on production - the Arab C, Arab D and Uwainat. Of these, the principal one is the Arab D, which currently produces 200,000 bopd, from a field total of 270,000 bopd (Dec. 95). It contains 200 wells - 130 producers and 70 water injectors, and is considered to be at a mature stage of development. The Arab D is roughly 210' thick and is composed of limestone - grainstone, packstone - except near the top and base, where dolomite is present. Fig. 2 (DK-66 log) illustrates a typical porosity-permeability profile, with porosities ranging between 10-25%, and permeabilities between 10-300 mD. It has been subdivided into ten flow units for reservoir simulation and volumetric purposes. An extensive gas cap is present above the oil column in the northern half of the field (fig. 3a). Here, the original gas oil contact (GOC) is at 6050' subsea, and the original oil water contact (OWC) at 6780' subsea, resulting in an oil column up to 730' in thickness. Field History Production History3 From the inception (1949), the Dukhan field underwent rapid development, reaching 175,000 bopd by 1962. This sudden explosion of oil production, together with the fact that the Arab D has only a very mild water drive mechanism, led to a severe drop in reservoir pressure. Using a datum of 6250' subsea, the pressure dropped from 3250 psi in 1950 to 2650 psi by the mid seventies. A peripheral pattern of water injectors was laid down to arrest/reverse the decline (fig. 3). This has been largely successful, as observed from the constant nature of the reservoir's pressure over the last decade. Production History3 From the inception (1949), the Dukhan field underwent rapid development, reaching 175,000 bopd by 1962. This sudden explosion of oil production, together with the fact that the Arab D has only a very mild water drive mechanism, led to a severe drop in reservoir pressure. Using a datum of 6250' subsea, the pressure dropped from 3250 psi in 1950 to 2650 psi by the mid seventies. A peripheral pattern of water injectors was laid down to arrest/reverse the decline (fig. 3). This has been largely successful, as observed from the constant nature of the reservoir's pressure over the last decade.