Case Study of Successful Matrix Stimulation of High-Water-Cut Wells in Dubai Offshore Fields
Authors: Shnaib Fathi Younis , Desouky Abdel Maksoud Mohamed , Mehrotra Nagendra , Kuthubdeen Mohamed Muhiz , Rutzinger Gunther , Judd Tobias Conrad , Rebello Raj Paul 
Published: March 2015

The candidate selection criteria, job design, and improved implementation techniques are important parameters for success in remedial acidization jobs in mature fields.

Effective acid diversion across heterogeneous carbonate reservoirs has always been challenging and is even more difficult when stimulating high-water-cut wells. For these types of wells, it is crucial to stimulate the oil-saturated layers rather than the watered-out layers. Bullheading conventional stimulation treatments tend to result in the aqueous-based stimulation fluid being injected into the high-water-saturated zones and away from the high-oil-saturated zones. This often results in a dramatic increase in water productivity and a minimal gain in incremental oil.

Recently, several of Dubai Petroleum's offshore oil wells have been treated using 15% hydrochloric acid (HCl) and a viscoelastic-surfactant (VES)-based diverter, resulting in a significant uplift in oil production and a decrease in water cut. The VES diverter permits the oil-saturated zones to be stimulated while minimizing the stimulation impact of the water zones, despite large permeability contrasts. This VES fluid is able to maintain its viscosity when in contact with water and it breaks when in contact with oil. The increase in production with decreasing water cut showed the success of this stimulation diversion technique.

This paper describes the candidate selection criteria, design, and implementation of successful carbonate matrix stimulation for high-water-cut wells in mature, water-flooded offshore fields.

Introduction

Matrix acid stimulation has been used for decades to increase the performance of oil, water or gas wells by removing or bypassing the near-wellbore damage, which was introduced over the course of drilling and production operations. Each stimulation job is unique and depends on the several factors that have to be taken into consideration before claiming success. Over the years, carbonate acid treatments have been designed to target stimulation of the hydrocarbon zone through the removal of near-wellbore damage and penetrating into the reservoir, creating wormholes. With mature high-water-cut fields, successful stimulation treatment involves reviewing the well history, reservoir characteristics, and potential production results before selecting the optimum stimulation treatment. In case the right stimulation treatment is not executed, there is a significant risk of increasing the water cut by stimulating the incorrect zone.

Dubai Offshore Environment

Dubai Petroleum operates four fields offshore Dubai, namely Fateh, South West Fateh, Falah, and Rashid fields which are in close proximity to Dubai, United Arab Emirates as shown in Fig. 1. The largest and the oldest field, Fateh, was discovered in 1966 and first produced oil in 1969. The field has been continuously developed since discovery and now includes its own processing, Waterflood and gas-lift compression facilities. South West Fateh was discovered in 1970 and is Dubai Petroleum's second largest field. Falah and Rashid fields were discovered in 1972 and 1973 respectively.

The production from these fields comes from three main carbonate reservoirs. A typical formation is comprised of a sequence of heterogeneous limestones overlaid and underlaid by shale formations. Four porous and permeable oil-bearing zones (named Zone 1 to 4 in this paper) have been identified within the formation and have been targeted for development for more than 30 years.