Real-Time Distributed-Temperature and Downhole-Pressure Surveying To Quantify Skin
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 155723, ’The Use of Real-Time Downhole Pressure and Distributed- Temperature Surveying in Quantifying the Skin Evolution and Zone Coverage in Horizontal-Well Stimulation,’ by Abdulelah A. Balto, SPE, Hassan B. Qahtani, and Khaled A. Kilany, Saudi Aramco, and Fernando Baez, SPE, and Tamer Elsherif, SPE, Schlumberger, prepared for the 2012 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 8-10 October. The paper has not been peer reviewed.

Fiber-optic-enabled coiled tubing (FOECT) has been used recently to evaluate reservoir-matrix chemical treatments qualitatively in real time. Attempts have been made to transform qualitative evaluations into quantitative ones. Pressure-transient analysis yields the skin value as a direct output, while the cooling-down/warming-up distributed-temperature-survey (DTS) profile identifies where treatment fluids went into the formation, hence identifying damaged zones. Combining well-test-analysis techniques with zonal-coverage evaluation is recommended strongly in highly deviated and horizontal wells in both clastic and nonclastic rocks.

Introduction

The near-wellbore rock matrix is where most of the permeability damage occurs from mud filtrate, adverse oil or water saturations, and clay migration. A sandstone-matrix treatment has multiple challenges including uncertainty in the lithology of the rock, uncertainty in damage identification, and secondary reactions that may cause blocking rather than stimulation.

A main challenge is obtaining uniform coverage of the treatment across the zone of interest. Therefore, the need for proper placement technique arises. Even though many diverting techniques have been developed in the past years, the challenge still exists in horizontal wells, especially with long sections that require optimizing placement of the treatment fluids, diverters, or reactive fluids. The complete paper details two challenges related directly to the operational side of stimulation: real-time, simultaneous fluid-placement optimization and treatment-effectiveness evaluation.

Case Overview

Well-A is a horizontal oil producer off-shore Saudi Arabia. The horizontal section extends approximately 3,400 ft in a clastic formation. The well was completed with inflow-control devices wrapped with a premium screen. It is believed that, since the beginning of production, the well has been underperforming and significant unwanted water is produced.

Challenges. As with most underperforming wells, several challenges are encountered in optimizing hydrocarbon production. Proper damage identification and appropriate treatment-fluid selection are critical enablers for success. The job design includes the placement technique, completion limitations, and any other factor affecting the success of the chemical treatment.

The evaluation process in long horizontal wells is slightly more complex than in vertical and deviated wells. The two main factors in such an evaluation are zonal coverage and skin reduction (i.e., gained pressure and, hence, a gain in production at the same outflow conditions).