Multiwell Case Study - Increasing Oil Production in a Mature Field With Rigless Intervention

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper IPTC 11644, "Increasing Oil Production in a Mature Field by Rigless Intervention-A Multiwell Case Study," by Vivek Garg, ONGC, and Shubhranshu Ashesh (now with Shell), SPE, Kapil Seth, SPE, and Amit Govil, SPE, Schlumberger, prepared for the 2007 International Petroleum Technology Conference, Dubai, 4-6 December. The paper has not been peer reviewed. Reviving production from brownfields is a major focus for oil and gas companies. Workflow and procedures are outlined that were adopted to increase oil production from seven wells by use of rigless intervention on an offshore platform off the west coast of India. Introduction The field was discovered in 1987 and was put on production in 1994. The main reservoir is a Middle Eocene carbonate deposit characterized by vugs, dissolution channels, and fractures (both vertical and horizontal). Hence, high-permeability streaks provide conduits for early water breakthrough, which has been primarily responsible for the decline in oil production. The average water cut in the field is 80%. The offshore platform posed a special challenge because of its proximity to two water-injector platforms. Injection-water accumulation in the drainage zone covered by the wells of this platform was determined by current temperature anomalies and salinity contrast between the formation water and the accumulated injection water in the vicinity of the wells. The challenge was to study the flow dynamics so that additional perforations in the bypassed section would yield water-free oil. Method The strategy included well diagnostics followed by workover intervention to increase oil production and reduce the water cut. Production logging identified the flow profile. Then, pulsed-neutron logging was performed where required to determine hydrocarbon (HC) saturation in the cased-hole environment. Integration of data from openhole logs, production logs, and pulsed-neutron spectroscopy helped identify depleted zones and zones of bypassed oil. Through-tubing isolation plugs were placed to isolate water-producing intervals. Oil in bypassed zones was accessed with additional perforations. Formation-water salinity was calculated from pulsed-neutron logging to identify zones of injection-water breakthrough. Such intervals were avoided when adding new perforations. Seven intervened wells yielded a 53% increase in oil production to 2,708 BOPD. The average water cut of the platform decreased from 80 to 76%. Candidate Selection The objective of the operation was to increase oil production while minimizing water and gas production. Because no rig was available, operations had to be carried out with a modular skid unit, which constrained available tools and methods.