A Novel Nonaqueous-Inhibitor Squeeze Package for a Water-Sensitive HP/HT Reservoir
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 87435, "The Challenge of Squeezing a Water-Sensitive HP/HT Reservoir - Lab and Field Experiences With a Novel Nonaqueous Inhibitor/Squeeze Enhancer Package," by Ping Chen, SPE, Thomas Hagen, Hugh Bourne, SPE, and Katherine Turner, SPE, Champion Servo, and Frank Moller Nielsen, Mette Rian, and Andreas Haldoupis, SPE, Statoil, prepared for the 2004 SPE International Symposium on Oilfield Scale, Aberdeen, 26-27 May.
Downhole scale control in Statoil’s Åsgard field presents a particularly severe challenge. The field is producing from low-permeability formations with a high drawdown through subsea templates. System pressure and temperature changes experienced during production promote formation of carbonate scales, which have been identified in the near-wellbore area and perforated intervals. The high formation temperature and pressure (165°C and 500 bar, respectively) and high chlorite content coupled with the water-sensitive nature of some of the formations create a challenging environment for downhole scale treatments.

Introduction
Oilfield scale is a water-related problem and often is associated with the production of water in the field. The severity of the problem and the most cost-effective solution are dependent on the field operating conditions. A number of remedial and proactive scale-management tools are available, including chemical- and nonchemical-based options. It is commonplace to prevent scale formation by injecting a chemical inhibitor continuously and/or by periodic squeeze treatments into the reservoir, depending on the location of the scale deposit. Åsgard is within the Haltenbanken group in an environmentally sensitive area because of its plentiful fish reserves, and licensees are faced with stringent guidelines for chemical use. The field comprises the Smørbukk, Smørbukk Sør, and Midgard fields. Åsgard is considered to be among the world’s largest subsea developments, producing oil, condensate, and gas through two production facilities (Åsgard A and B) from 10 reservoirs spread over a 60×20-km area. The production facilities include 50 wells in 16 subsea templates tied together by 300 km of 10- and 20-in. flowlines. Carbonate-scale deposition has been identified in the near-wellbore area and in tubing for some of the wells in Åsgard.
Production conditions in the Smørbukk field present the greatest challenge for carbonate-scale control. All Smørbukk producers are commingled, with production from several formations. The high pressure and high temperature (HP/HT) and the environmental requirements limit the choice of chemistry that can be used. In addition, the field is producing from low-permeability formations with a high drawdown through subsea templates, which increases intervention complexity and the potential for and impact of formation damage. Some of the Åsgard formations are rich in fines, and additional precautions are required when deploying fluids into the near-wellbore area to minimize fines mobilization.