Sand Management on the Lunskoye High-Gas-Rate Platform: Quantitative Risk Assessment

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 112099, "Applying Sand-Management Process on the Lunskoye High-Gas-Rate Platform Using Quantitative Risk Assessment," by M.C. Gunningham, SPE, Sakhalin Energy Investment Company; M.A. Addis, SPE, Shell; and J.A. Hother, SPE, Proneta UK, prepared for the 2008 SPE Intelligent Energy Conference and Exhibition, Amsterdam, 25-27 February. The paper has not been peer reviewed. Quantitative risk assessment (QRA) was applied to sand management in the Lunskoye field to minimize risk of failure while maximizing production, reducing cost, and safeguarding reserves. Lunskoye is a high-rate gas development offshore Sakhalin Island. This work has reduced the project risk exposure significantly, while reducing well-completion costs and safeguarding production in the long term. Introduction The Sakhalin Phase-2 development comprises two new offshore platforms, one on the Lunskoye field and the second on the Piltun field. The Phase-2 development also includes changing the existing Astokh platform to a year-round production operation. These platforms will be linked to an oil terminal and a liquefied-natural-gas (LNG) plant 800 km away on the southern edge of Sakhalin Island. More than 90% of the gas for the LNG plant will be supplied by the Lunskoye field (Fig. 1). The Lunskoye field is in 48 m of water in the Sea of Okhotsk, east of Sakhalin Island. The potential of sand production disrupting gas production and LNG delivery was minimized in the design stage of the project. The full-length paper details a QRA based on the as-built Lunskoye-A facilities and updated well and completion designs. The aim was to reduce residual risks further by identifying and quantifying the critical failure modes and identifying appropriate mitigating measures by use of a systematic rigorous methodology based on sound principles, which is able to provide implementable results. Completion Design and Predicted Sand Production This QRA of the Lunskoye-A wells and production facilities focused specifically on failure modes resulting from sand production. Sand production occurs when the reservoir effective stresses exceed the strength of the sandstone, resulting in rock failure and disaggregation, during which sand grains become detached from the sandstone. The effective stress in a reservoir increases during depletion, causing the weaker sandstones to fail, followed by the failure of successively stronger sands as depletion continues. If the disaggregated sand is transported to the facilities in the gas and liquid stream, it will result in erosion of the flowlines and will settle in areas of low flow velocities, leading to plugging. If the sand is not transported out of the wellbore and remains in the well, the completion interval will gradually "sand up" and production will decline, requiring a workover and a cleanout to restore productivity.