New Acidizing Method Improves Stimulation in Deep, High-Temperature Offshore Well
Authors: Feder Judy 
Published: June 2020

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 196281, “Acidizing Done Right in Hot Offshore Wells: Case Study,” by Max Nikolaev, SPE, Bulat Kamaletdinov, and Nestor Molero, SPE, Schlumberger, et al., prepared for the 2019 SPE/IATMI Asia Pacific Oil and Gas Conference and Exhibition, Bali, Indonesia, 29-31 October. The paper has not been peer reviewed.

The complete paper discusses a method of stimulating deep, high-temperature offshore wells by combining an efficient single-phase retarded acid (SPRA) system and an engineered, degradable, large-sized particulate and fiber-laden diverter (LPFD). The method was introduced in a well in the Arabian Gulf, where it helped the operator achieve effective, uniform stimulation.

Introduction

Treatment of deep, high-temperature carbonate reservoirs such as those in the Arabian Gulf presents a series of complex and related challenges to achieve effective and uniform stimulation. Elevated temperatures and heterogeneous formations in these reservoirs require robust treatment fluids that can withstand the harsh environment to achieve good reservoir contact with an acid system along the entire interval of interest.

Emulsified acids have been the preferred stimulation choice of major operators in this region because of these acids’ superior corrosion inhibition and deeper penetration into the reservoir. However, using emulsified acid adds to the complexity of the stimulation operation by contributing to higher friction pressures, limiting pump rates, and requiring elaborate mixing procedures that constrain offshore rig-based interventions. Operators are searching for simplified acid systems that can deliver friction pressure similar to that of unmodified hydrochloric acid (HCl) and reservoir contact performance equivalent to that of emulsified acid. Arabian Gulf operators also seek a robust diverter that can withstand high differential pressure at high temperature, enabling efficient treatment coverage of all perforated intervals.

Previous stimulation jobs in the region indicated a need for a significant amount of traditional diversion materials to effectively plug the leakoff zones. To address the challenges, an SPRA and a new degradable LPFD system were introduced to conduct a matrix-stimulation treatment featuring efficient contact with the reservoir, safe corrosion inhibition, and effective diversion in a well with a 320°F bottomhole static temperature and a heterogeneous environment with a permeability contrast of more than 100. The SPRA was a 15% HCl-based acid system.

The fluid delivered friction pressures similar to those of unmodified 15% HCl and wormholing performance equivalent to that of emulsified acid without encountering the issues of fluid quality with respect to emulsion stability, and much higher dissolution power than organic acids and chelating agents. The pressure drop after the first acid stage was greater than 1,000 psi in approximately 60 minutes. After the second stage of acid, the pressure drop was close to 1,000 psi in approximately 30 minutes, achieving an approximately 1,000-psi increase of injection pressure across the perforations. Additionally, using the LPFD system reduced the footprint in offshore operations, simplified materials handling, and delivered the most efficient diversion performance in bullhead operations compared with that of other diverters.