Abstract
A new technique for zone isolation in horizontal wells has been proposed. The new technique consists of three sequential stages: (i) setting a chemical wellbore plug in the horizontal section upstream of the zone to be isolated, (ii) spotting a gel just downstream of the wellbore plug and squeezing the gel into the zone to be isolated, and (iii) washing or drilling through excess gel and the wellbore plug to clean the borehole prior to production. The main objective of this research is to investigate the feasibility of setting a chemical wellbore plug in a horizontal wellbore. Two main problems associated with the wellbore plug were investigated: (a) method of placement of the plug so that slumping would not occur, and (b) selection and testing of chemicals that could be used to make wellbore plugs with sufficiently high holding pressures. Three chemicals, used in the oil industry for gas and/or water shut-off, were selected for the study. The commercial names of these chemicals were SEAL, PERMASEAL and TEXPLUG. Experimental apparatus were designed and constructed to study placement techniques and to measure the holding pressures of the wellbore plugs. The horizontal wellbore models consisted of PVC pipes internally lined with sand. The X-ray CT scanner was used to obtain cross-sectional images of the plug to help understand the shear mechanisms involved. The experimental results indicate that a plug could be placed in a horizontal wellbore with minimum slumping, if the plug is introduced into a viscous completion brine pill. For TEXPLUG, a suitable completion brine would contain 100,000 ppm NaCi and 4 lb/bbl CMC (carboxyl methyl cellulose). Further, results indicate that only TEXPLUG has a sufficiently high holding pressure (about 340 psi for 37 in. long, 1 in. I.D. plug) necessary for a wellbore plug. Based on experimental results, the proposed new isolation technique appears to be viable. However, further experimental studies are required, particularly to evaluate the effectiveness of the wellbore plug in conjunction with displacement of formation gels.
Saavedra, Nestor Fernando (1996). Chemical wellbore plug for zone isolation in horizontal wells. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -S22.