Intervention Work Flow Improves Injection Coverage in Tight Carbonate Reservoirs
Authors: Feder Judy 
Published: June 2020

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 199290, “Advanced Intervention Work Flow Brings High-Pressure Jetting to New Heights of Effectiveness and Enables Unprecedented Injection Coverage in Tight Carbonate Reservoirs,” by Samy Mohamed Abdelrehim, Daniel Gutierrez, and Sameer Punnapala, SPE, ADNOC, et al., prepared for the 2020 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, 19-21 February. The paper has not been peer reviewed.

The complete paper discusses an advanced matrix-stimulation work flow that brings reliability and flexibility to the acidizing of tight carbonate water injectors and has delivered injectivity improvements tight carbonate onshore reservoirs in the Middle East. The work flow leverages real-time downhole measurements and the presence of fiber optics in coiled tubing (CT) for telemetry, and relies on a high-pressure jetting tool, controlled with the help of real-time downhole pressure data, to enhance penetration of acid into the targeted intervals.

Introduction

Effective and long-term matrix stimulation of water-injector wells completed across tight carbonate reservoirs presents a significant challenge in the Middle East. Local practices for matrix stimulation of openhole horizontal carbonate water injectors consist of spotting hydrochloric acid treatment by CT along the uncased well section, using a specific fluid dosage per unit length of the pay zone. Thus far, that approach has delivered inconsistent results in wells completed across tight carbonate rock, most often leading to a rapid decline in injection rates following the treatment.

An alternative work flow leverages distributed temperature sensing (DTS) to evaluate the original water-injection coverage across the reservoir. Each section benefits from a customized treatment that increases injectivity and improves uniformity of injection. A high-pressure jetting tool, controlled with the help of real-time downhole pressure data, is key to this work flow because it enhances penetration of acid into the targeted intervals. The engineered work flow has delivered injectivity improvements of nearly 8,000 B/D in the intervened wells, with the DTS survey confirming significant gains in injection coverage along the openhole section.

The complete paper is organized into three sections - matrix stimulation challenges, proposed solution, and case studies.

Matrix-Stimulation Challenges

Unsuccessful acidizing treatments in carbonate formations usually have a common denominator: poor zonal coverage of the pumped stimulation chemicals. In water-injector wells, efficient reservoir sweep relies on understanding the optimal distribution of the stimulation fluid to maximize the water-injection capacity of the well.

Understanding heterogeneity is fundamental for successful water injection in a carbonate reservoir. The presence of a dominant zone, also called the thief zone, is one of the most-obvious manifestations of heterogeneity, usually pointing to a layer with higher permeability than the average reservoir permeability. This heterogeneity leads to nonuniform injection profiles. Consequently, reservoir sweep by water becomes inefficient, leaving significant residual oil behind, risking creation of unwanted pressure differentials in the reservoir and leading to early water breakthrough in nearby producer wells. Fig. 1 shows the downhole intake profile for one water injector well from Field B. A nonuniform distribution of injection water across the uncased horizontal section is featured clearly, with almost all injected fluid going through the middle section [10,886 to 11,480 ft measured depth (MD)], leaving almost 75% of the open hole bypassed. The matrix-stimulation approach should be rethought to address the presence of thief zones.