Experimental study of zone isolation in horizontal wells using a new straddle-chemical-wellbore-plug system

Abstract

This research constitutes part of phase II of a joint industry project aimed at investigating the feasibility of sealing off water and gas producing zones in a horizontal well. This research is a follow-up from an earlier joint industry project (phase 1) to study the use of chemical wellbore plugs for zone isolation.' The earlier experiments were conducted using PVC pipes up to 2-in. diameter and 3-ft. length. The encouraging results from these earlier experiments led to testing the method in a full-scale 60-ft. long by 6-in. diameter wellbore model. The new method consists of four sequential stages: (i)Setting a chemical wellbore plug in the horizontal section just upstream of the problem zone. (ii)Setting a second chemical wellbore plug in the horizontal section downstream of the problem zone. (iii)Spotting and squeezing a low viscosity formation gel between the straddle wellbore plug system into the problem zone. (iv)Washing out excess formation gel and wellbore plug to clean the borehole prior to production. The . job would be carried out using coiled tubing and only one round trip would i be necessary. The objective of this research is to investigate the feasibility of the new straddle-chemical-wellbore-plug system using a full-scale horizontal wellbore model subjected to a reservoir temperature of 120 OF. Two chemicals, namely K-MAX and PERMSEAL were used, and in the experimental run, a 40-ft. long chemical wellbore plug (K-MAX) was set, followed by injection of formation gel (PERMSEAL) into a 20-ft. zone. From symmetry, the system represented an actual straddle chemical plug pair, each up to 40-ft. length and a 40-ft. zone into which formation gel is injected. Based on results from the first run, the new straddle-chemical wellbore-plug system appears to be a viable method. The chemical plug sealed the pre-perforated liner/sand-screen annulus completely off, and the formation gel had penetrated the sand, making it very consolidated and impermeable. These initial results indicate great promises for the new straddle-chemical-wellbore-plug system. Further experimental runs are however required to fully test and optimize the new zone isolation technique.