Sand Production in the Statfjord Field

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 97794, "The Relative Importance of Drawdown and Depletion in Sanding Wells: Predictive Models Compared With Data From the Statfjord Field MM," by M.H. Hettema, SPE, J.S. Andrews, SPE, and M. Blaasmo, SPE, Statoil ASA, and E. Papamichos, SPE, SINTEF Petroleum Research, prepared for the 2006 SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, 15–17 February. Sand-production behavior at Statfjord field can be described as controlled by two sand-production regimes, one controlled by shear failure and the other controlled by rate. Study results show that sand production will limit well production rates for most formations and that sand control is needed to ensure high production rates during the late-life development of the field. Introduction The Statfjord field is a large oil field in the northern part of the Viking Graben and straddles the border between the Norwegian and U.K. sectors. The field has been in production since 1979, and both waterflood and gas injection have been used for secondary recovery. More than 65% of the original oil in place has been recovered. The Brent and Statfjord producing reservoirs consist of weak to intermediate-strength sandstone. The strategy used for many years is that produced sand is handled topside before on-site disposal. Producers are completed with a perforated liner and many have produced sand in a controllable manner from the time they came on stream. Because deep depressurization to produce solution gas is planned for late-life development, the study detailed in the full-length paper was performed to determine how the planned reservoir-pressure depletion will influence sand and field production. Yearly sand production on each platform is estimated to be 50 to 100 tons. In the acceptable-sand-rate (ASR) test, the production rate is determined at which no more than 0.015 L of sand is produced in the sand trap during a 2-hour test. Because many producers are operated by an ASR criterion, field production is strongly related to sand production. If the planned reservoir depressurization leads to significantly more sand production, this would have unacceptable consequences for late-life production from the field. Empirical Sand-Production Criterion Sand production can be regarded as a three-step process:rock-matrix failure,erosion of the failed material, andtransport by fluid flow through the well. These steps are controlled by cohesion breakdown, drag forces, and well hydraulics, respectively. Extensive production experience from Statfjord was used to determine how reservoir-pressure depletion will influence sand production. Critical drawdown pressure is defined as the drawdown pressure at which the ASR wells are tested and operated. To analyze field data, an empirical sand-production criterion relating the critical drawdown pressure, pcd, to reservoir pressure, pR, was used.