Monitoring of Matrix Acidizing by Use of Resistivity Measurements
Authors: Carpenter Chris 
Published: July 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181414, “Monitoring of Matrix Acidizing by Use of Resistivity Measurements,” by Mehdi Ghommem, American University of Sharjah, and Xiangdong Qiu, Dominic Brady, Firas Al-Tajar, Steve Crary, and Alaa Mahjoub, Schlumberger, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed.

This paper describes the testing of a novel concept based on resistivity measurements to monitor acid-stimulation operations. It is believed that the proposed concept for monitoring the wormholing process can be adopted in the field with the deployment of induction tools. The outcome of this novel monitoring concept is expected to provide an unprecedented level of understanding of the depth, number, and type of wormholes being created downhole.

Introduction

Induction-logging tools can be viewed as an attractive option for characterizing wormhole morphology resulting from the acidizing process and can be used to assess acid-stimulation operations. The authors propose to extend the use of resistivity-logging tools for evaluating acid-stimulation jobs after well cleanup. This concept relies on the significant variations in the electrical resistivity of the different fluids and chemicals involved in the acidizing process and the increase in the effective porosity in the near-wellbore region resulting from the acid reactive dissolution. In this work, the authors conducted resistivity measurements while acidizing carbonate core samples. To do so, an electrically sensitive coreflooding setup was designed to conduct acidizing tests of carbonate core samples while measuring the change in the electrical resistivity at multiple points along the core and in real time. The paper shows the potential use of such measurements to monitor wormhole penetration and branching in real time. A yard test was conducted to verify the response of a real induction tool to simulated wormholing features.

Resistivity Measurements While Coreflooding

Experimental Setup and Procedure. A three-phase methodology was followed: rock-sample characterization, coreflooding and resistivity measurements, and characterization of the core samples after acidizing to inspect the wormhole structure and invert through the model to close the experimental loop.

Saturation of Cores and Porosity Measurement. The core samples were put under a vacuum for a few hours and weighed. Then, they were saturated with 50,000 ppm of sodium chloride (NaCl) at a pressure of 2,000 psi for a few hours. After saturation, the samples were weighed again; the difference in the weight of dry and saturated samples was simply converted to the pore volume of the rock.

Permeability Measurement. The permeability of the rock samples was measured by the constant-flow-rate method. This was performed by flowing deionized water across the cores in the coreflooding system while recording the pressure drop. The permeability was computed from the pressure drop and corresponding flow rate using Darcy’s law.