Failures and Remedial Measures for Cementing Vertical Shale Gas wells in India – Case histories

Abstract

Abstract This paper discusses case histories with solutions-oriented approach to shale gas cementation problems. Shale gas exploration and production around the globe in general, and US in particular has witnessed surge in activity to the extent that Shale gas is often regarded as ‘a game changer’ in the hydrocarbon industry. The success in United States has prompted the governments of several countries to develop their own shale gas programmes. In India, estimates of shale gas resources vary from 63 Trillion Cubic Feet by Energy Information Administration (US). In order to tap this resource, Government of India came out with a Shale Gas and Oil Policy in 2013. Consequently, ONGC and OIL were given blocks mainly in Gujarat to test shale production technology and potential. ONGC drilled 1st shale gas well # JMSGA of Jambusar field and well # GNSGA of Gandhar field, Cambay basin successfully. But CBL - VDL shown very poor results. After this failures, two more shale gas wells were awarded to service provider to carry out cementation for GNSGC and GNSGB wherein the cement slurries were used by adding proprietary chemicals. Results shown some improvement in CBL-VDL against shale gas. Poor CBL-VDL creates a problem in production operation both for geothermal wells and oil wells. To accomplish good cement bond, complete removal of mud /all well fluid is necessary to enhance the displacement efficiency by maintaining desired rheological properties. However, in spite of this, many times the cement bond leading to poor bonding/ insufficient zonal isolation. As a part of strategic planning it was decided to develop in house innovative expertise to solve the problems. Accordingly an extensive experimental analysis were carried out specially using expanding additives (3-5% bwow) in cement system, exhibited improved properties like Right Angle Set, Compressive strength, Stability, fluid loss control and desired rheology. Practically, combinations of salts in cements and spacers in pre flushes in cementing fluids have provided means for managing shale instability. Learning experience from past utmost care was taken for optimization of rheological hierarchy for mud, spacer and cement using fluid friction chart and cement software shown a phenomenon improvements in achieving desired parameters. The field trials have been carried out successfully in three shale wells in India. 1st Well # TVAU of Cauvery and recorded excellent CBL-VDL (1-2 mV) against shale gas. 2nd Well # WDAU of Ahmedabad. Achieved excellent slurry/spacer parameters.3rd Well # ROBB of Agartala for 5-1/2" casing cementation resulted in better CBL-VDL (02-07mV) against shale zones. These innovative techniques are cost effective, easy to handle and technically suitable. Also establishes in-house technological advancement in designing cement slurries and become a proven approach for cementing Shale gas wells in near future.