Abstract

In this paper we present details of a coiled tubing stimulation treatment utilising a non- damaging self-diverting surfactant based acid system. The technology was used to maximise coverage over a 3100 ft 8 ½" open hole interval designated to receive UeR aquifer water in order to maintain reservoir pressure in the Arab D oil reservoir. The system was employed as it offered a number of benefits over alternative acid systems employed previously offshore Qatar. These systems include self-diverting polymer based acid systems as well as foams and emulsified acids. It is best practice to flow back a well after acidizing prior to placement on injection in order to remove damaging components of the treatment fluid and any undissolved residual rock debris. However, in many cases this is not practicable as the reservoir pressure is often not high enough to facilitate treatment flow back and artificial lift is required. Moreover, such flowback practices require additional facilities to be placed on the rig to handle spent acid and create extra risk from a health and safety standpoint. We present details of the surfactant based system and its several benefits including the ability to maximise diversion through in-situ viscosification and to completely destroy the spent acid gel created using a mutual solvent overflush and subsequent dilution with water. We present a case history which demonstrates the effectiveness of the treatment through comparison of expected injectivity, using numerical reservoir simulation, and actual post stimulation injectivity: a two fold increase in injectivity index was observed. We highlight other environments where this technology is applicable and also describe limitations of such treatments.

Introduction

Challenges in Stimulation of Long Open-Hole Horizontals.

Long open-hole horizontal intervals represent a significant challenge for stimulation. The benefits of horizontal wells to maximise hydrocarbon recovery and induce a more uniform reservoir sweep have long been recognised in the industry. There have been many technical and economic challenges encountered in the drilling and completing of long horizontal wells. Acidizing of carbonate intervals is a recognised technique to bypass drilling damage in the near well-bore region. The major challenge for the industry has been the efficient placement of acid along the entire length of the drilled interval. On many occasions a simple bullheading technique has been found to produce a significant increase in injectivity index but exacerbate reservoir sweep with the majority of fluid injection only occurring across a small portion of the interval.

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