No abstract

Calcium carbonate scale threats for deepwater developments have been predicted by calculating the saturation ratio (SR) and mass of calcium carbonate. Assessing the threat scale may pose to an operation allows the design and implementation of robust barriers to reduce the risk. Scale threat assessment is particularly important in the early phase of a project when options for controlling the threat are being evaluated. It is important to correctly interpretate scale prediction result and its operational significance in terms of the threat likelihood and severity. Widely adopted guidelines, based on industry experience built up over many years from operations in US land and in the North Sea, have been used to aid interpretation. However, the relevance of these guidelines for deepwater projects has long been challenged. The relationship between predicted SR and mass of calcium carbonate in deepwater is explored. Through case studies, it is apparent the current guidance is not stringent enough for deepwater. Additional guidance for deepwater operations is proposed. This paper describes the deepwater operational experience that was used to justify a change in the critical SR and mass values in the scale threat assessment guidelines now adopted to assess the likelihood of scaling in deepwater fields.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDown-hole scale control in Statoil's Åsgard field presents a particularly severe challenge. The field is producing from low permeability formations with a high draw down, through subsea templates. System pressure and temperature changes experienced during production promote the formation of carbonate scales, which have been identified in the near well bore area and perforated intervals. The high formation temperature and pressure, 165 o C and 500 bars respectively, high chlorite content coupled to the water sensitive nature of some of the formations creates a challenging environment for downhole scale treatments. This paper will describe possible formation damage mechanisms that were identified for this water sensitive formation and the treatment strategy adopted to minimize them. It also presents the extensive laboratory studies that were undertaken to develop a non-damaging, non-aqueous inhibitor/squeeze enhancer formulation suitable for deployment under these harsh conditions. An understanding of the mechanisms by which the squeeze treatment package prevented water block formation and clay mobilization under such severe temperature and reservoir constraints, coupled to the mechanisms of squeeze life extension are discussed. The paper will also highlight the manufacturing challenges that were overcome to improve the environmental profiles of the products.The paper will finally discuss the two treatments, which have been performed to date with the non-aqueous products. Initial field data demonstrates that the application of this nonaqueous product package significantly reduced the potential for formation damage and allowed the successful treatment of these wells. Residual inhibitor returns remain significantly above MIC and a long squeeze life is expected for both wells.