Assessing Fluid Migration and Quantifying Remaining-Oil Saturation in a Mature Carbonate Reservoir
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper IPTC 13503, ’Assessing Fluid Migration and Quantifying Remaining-Oil Saturation in a Mature Carbonate Reservoir: Dukhan Arab D,’ by Levin Barrios Vera, SPE, Tajjul Ariffin, Ali Trabelsi, Ibrahim Al-Qarshubi, and Hussain Abdulla Al-Ansi, SPE, Qatar Petroleum, prepared for the 2009 International Petroleum Technology Conference, Doha, Qatar, 7-9 December. The paper has not been peer reviewed.

The large mature Dukhan field is onshore Qatar. It is believed that differential depletion resulted in considerable fluid migration across sector boundaries, which introduced uncertainty in quantifying the remaining oil in place, recovery efficiency, and reserves. Conventional material-balance and volumetric techniques were used to investigate the reservoir behavior to assess fluid migration, current oil in place, and recovery efficiency, and to identify limitations and uncertainties. 

Introduction

The main oil reservoir in the Dukhan field is the Arab D. Development of the reservoir was from north to south, creating differential-pressure depletion between two of the southern sectors of the reservoir. Developing the remaining oil in some areas of the Arab D reservoir will depend largely on understanding the fluid migration. As part of ongoing reservoir studies, conventional material-balance and volumetric analyses were carried out to characterize the current drive mechanism and quantify fluid migration between reservoir sectors.

Dukhan Arab D Reservoir

The Dukhan field is approximately 80 km west of Doha. Discovered in 1941, production commenced in 1949. The field has more than 750 well penetrations. The major oil reservoirs are the Upper Jurassic Arab C and Arab D.

The Arab D reservoir has four interconnected sectors: Khatiyah, Fahahil, Jaleha, and Diyab. The division into sectors is based on allocation of wells to surface facilities. The northern sectors, Khatiyah and Fahahil, contain saturated oil with a large gas cap. The Jaleha sector contains saturated oil, and the southernmost sector, Diyab, is undersaturated.

The reservoir rock comprises limestone and dolomite, with high-permeability grainstone layers, particularly in the upper section. The average thickness is 200 ft, with average porosity and permeability of 19% and 100 md, respectively. Arab D historical production can be divided into three periods.

Primary production under natural depletion from1949 to 1970

Gravity (“dump”) waterflooding from 1970 to 1990

Powered water injection from 1990 onward

Development from north to south created differential-pressure depletion between the Jaleha and Diyab sectors. The Diyab-sector pressure declined 350 to 400 psi before commercial production commenced in 1976.

Fluid Migration

Future development of the remaining oil in the Jaleha and Diyab sectors requires understanding the fluid migration and reservoir structure. Because of uncertainties in structure and fluid content, the transition area between these two sectors is relatively undeveloped, with only a few vertical wells.