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Implementation of Through-Tubing Technology in a Challenging Offshore Environment

Topics: Offshore
Fig. 1—Gauge-survey interpretation plot. TVDSS=true vertical depth subsea.

A well drilled and completed in a marginal field offshore India produced only gas until the oil-bearing sands were perforated and the well was put on commingled-oil-and-gas production. Through-tubing sand control was installed in the well, but, over time, formation pressure depleted and the well eventually died. The challenge was to unload and activate the well by use of gas lift in a commercially viable manner, avoiding expensive barge-based operations.

Well History

The LG field was the first commercial discovery in the XY Block, 10–15 km west of the Hazira coastline in the Gulf of Khambat. The field is approximately 38 km2 in an area ranging in depth from 10 to 25 m. The area experiences harsh sea conditions, with 6- to 8-knot underwater currents and tides of up to 6–8 m. The seabed channels and bars shift continuously. The seawater is extremely muddy, with near-zero visibility. The field contains excellent-reservoir-quality sands with porosities of 28 to 33% (average is 30%) and permeability of up to 4 darcies (average is 1.5 darcies). The field contains light sweet crude oil with gravity ranging from 38 to 45 °API. The undersaturated crude has a solution-gas/oil ratio in the range of 400 to 500 scf/bbl. Initial reservoir pressure in most of the reservoirs within the field ranges from 1,700 to 1,800 psia. Bubblepoint pressure is in the range of 1,600 to 1,700 psi. Because of the relatively high bubblepoint pressure, most of the sands are saturated.

LG was discovered initially as a gas field, and the wells were drilled and completed as gas wells across its various subdivided units on a lithostratigraphic basis. Well AB-5 was drilled and completed as a single selective two-zone completion. Because the field orientation was toward producing gas, tandem expandable shelter systems (ESSs) were deployed against the upper and lower sands (gas zones) with an inflatable isolation packer on the blank pipe between ESS sections. As permission was granted only to produce gas, provision was kept for possible future access to the lower oil-bearing sand. The well was put on commingled gas production from the B2 and B1 upper zones. The well eventually began producing water from the B zones; hence, it was decided to perforate the T1L oil-bearing sand for production. The well was perforated in February 2007 and was put on oil production. Because there was no sand control installed against the oil zones, the well was being produced with limited drawdown to avoid sand production. This was also accomplished in hopes of obtaining a sand-free production in absence of any sand control for other wells drilled and completed with a similar approach. Continuous sanding was observed post-perforation, which resulted in sand fill-up across the newly perforated oil sands. The well was immediately shut in, and several bailer runs were conducted to clear off the sand deposition against the perforation interval.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 24784, “Successful Implementation of Through-Tubing Technology (Sand Control and Gas Lift) in a Challenging Offshore Environment as an Integrated Development Strategy for Sustainable Development of Marginal Fields: A Case Study,” by Anurag Sharma, Alok Kumar Singh, Saurabh Anand, Arunabh Parasher, and Amit Sharma, Cairn India, and Sagar Kale, Weatherford, prepared for the 2014 Offshore Technology Conference Asia, Kuala Lumpur, 25–28 March. The paper has not been peer reviewed. Copyright 2014 Offshore Technology Conference. Reproduced by permission.
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Implementation of Through-Tubing Technology in a Challenging Offshore Environment

01 November 2014

Volume: 66 | Issue: 11

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