Experimental Investigation of Sanding Propensity for the Andrew Completion
Authors: Venkitaraman A. , Li H. , Leonard A.J. , Bowden P.R. 
Published: March 2010

One of the main concerns during the completion phase of the planned Andrew horizontal wells was sand production. Analytical models based on inputs from log details and core analyses favoured the use of perforated, cemented liner completions to lessen the likelihood of sand production. To further strengthen this recommendation and to perform a risk analysis of formation failure at the time of underbalance perforation and expected producing conditions, laboratory experiments were conducted on three reservoir core samples selected from two pilot wells. The core samples were perforated with shaped charges under simulated downhole conditions. The perforated core samples were flowed, while monitoring any sand production resulting from the effects of increasing rate (change in drawdown), onset of water cut and depletion (increasing effective stress).

The core samples did not show any propensity to produce sand during single-phase oil flow (rates of up to 20 cm3/s/perforation). When water cut was introduced, transient sand production was observed, indicating the production of perforation-generated rock debris. As the percentage water cut was increased, the sand production declined. The core samples did not show any propensity for sand production during depletion testing. The wells were subsequently completed with perforated cemented liners with no sand control. Now, into two years of production no sand problems have been encountered. These experiments are presented as a means of complimenting existing sand prediction models in completion designs for sand prevention.

Introduction

The Andrew oil field, located in the central North Sea, is operated by BP Exploration. Oil is produced from a Palaeocene sandstone reservoir. The reservoir, at around 2,500 m below sea level, is normally pressured, with a 58-m oil column between gas cap and aquifer. Based on achievement of expected economic return, an all-horizontal field development was designed(1). However, one of the major concerns was the possibility of sand production from sandstone shear failure at the wellbore wall or from water cut. Considering the impact of a choice between sand control and sand prevention on the economic success of the development, a reliable sand production risk analysis was needed prior to completion of the wells.

In general, available sand prediction models can be classified into:core-based models [Brinell hardness tests, unconfined compressive strength (UCS) tests, thick walled cylinder tests (TWC), etc.];log based models; and c) regional statistical sand production models(2).

Several case studies are available where these have been applied in the field(3). Following a similar approach, log data from an Andrew appraisal well were processed to obtain UCS values. Core samples at different intervals from the same well were used to conduct UCS and TWC tests. Empirical relationships developed by BP in conjunction with numerical analyses were used to assist in core test data interpretation. The mean Andrew rock strength was determined to be 16.1 MPa UCS, which lies between the Forties reservoir sandstone (1.05 - 2.8 MPa UCS), which produces significant volumes of sand, and Cyrus (25.2 - 35 MPa UCS) which produces sand-free, even after water cut.