Chemical-Diversion Agents Can Aid Acid Fracturing in Openhole Horizontal Wells
Authors: Feder Judy 
Published: May 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE-191415-18IHFT-MS, “Experimental Investigation on Tool-Free Multistage Acid-Fracturing of Openhole Horizontal Wells Using Diversion Agents,” by Jianye Mou, SPE, and Shaodan Tao, China University of Petroleum-Beijing; Xuezhi Hui, CNPC; and Lei Wang, Shicheng Zhang, and Xinfang Ma, China University of Petroleum-Beijing and State Key Laboratory of Petroleum Resources and Prospecting, prepared for presentation at the 2018 SPE International Hydraulic Fracturing Technology Conference and Exhibition, Muscat, Oman, 16–18 October. The paper has not been peer reviewed.

In openhole horizontal wells in high-temperature, naturally fractured, deep formations, mechanical segmentation between stages for multistage fracturing operations is high-risk, costly, and sometimes ineffective. Acid fracturing using chemical diversion agents as an alternative to mechanical segmentation has been pilot-tested in some fields with satisfactory results, but the technique has not been studied experimentally or numerically extensively before now. This paper presents a newly designed triaxial fracturing system and describes a series of experiments that verified the validity of tool-free chemical diversion for multistage fracturing of openhole horizontal wells.

Introduction

Traditional staged fracturing technologies include double-pack single-slip multistage fracturing, packer/sliding-sleeve fracturing, and hydraulic-jetting multi-stage fracturing. These technologies use tools to achieve segmentation between stages. The tools are neither effective nor reliable under some circumstances such as multicluster fracturing inside a stage; refracturing of horizontal wells; and in deep, high-temperature, vuggy, naturally fractured formations. Diverted fracturing with chemical diversion agents has become an option.

Diversion has been applied in matrix acidizing and, more recently, in fracturing. Diverted fracturing can be used for both far-field and near-wellbore diversion. Far-field diversion shifts the fracture to unstimulated areas to create complex fractures that increase reservoir contact volume. This paper focuses on near-wellbore diversion, which can be accomplished using mechanical and chemical methods.

Recently developed chemical diversion materials include ball sealers, particulates of various sizes, and fiber. These diverters need to be degradable or dissolvable in formation fluids over time. Particulate diverters are available in sizes ranging from several millimeters to a micrometer, allowing them to plug orifices of various sizes and to bridge perforations, fractures, and vugs. Degradable fiber is another commonly used diverter. It can bridge the fracture or fill the gap between particulate diverters to form a tight barrier. Combinations of particulate diverter and fiber have been used often.

Diverted fracturing has been used in horizontal wells for refracturing, fracturing multiple clusters in one stage, and even for segmentation in openhole horizontal wells. Refracturing targets regions that have adequate reserves for recovery but are underdeveloped because of non-uniform cluster stimulation. Chemical diversion can restimulate these reservoirs.