The Challenges Associated With Performing and Combining Scale Dissolver and Squeeze Treatments in Kristin—A Subsea HP/HT Gas Condensate Field

Abstract

With an initial reservoir pressure of 911bar and a downhole temperature of 170 o C Kristin is the first HPHT field in the world that has been completed and produced using subsea solutions. CaCO 3 scale has been identified as the major production problem due to the expected high draw down from the reservoir together with the high level of bicarbonate and calcium in the formation water. In April 2007 breakthrough of formation water in two of the wells were detected and the subsurface safety valve in one of them showed increasing inertia. In August/September 2007 the first combined scale dissolver & squeeze treatments were carried out in these two wells. This culminated after more than 5 years of testing of a large variety of chemicals and operational planning. The jobs were successfully carried out using the unique HP injection system on board that is dedicated for such well intervention. In this paper a full case history of these first treatments on Kristin will be presented. It starts with a brief summary of the difficult path to qualify various chemicals for the challenging conditions. This is followed by the early detection, diagnosis and data interpretation processes when the formation water first broke through. The paper will include the operational planning with special focus on the constraints to inject chemicals at an adequate rate against a HPHT well. The challenges in delivering and maintaining separation of the different chemical pills to a well lying 7km away will be highlighted. Despite the best intension some compromises on the treatment design have to be made in order to maintain safety and system integrity and these will be discussed. Finally the paper will conclude by presenting the results from these treatments, the assessment of the operations, the experiences being learnt and the area identified for future improvement.

Solubility of Barium Sulfate in Formate Brines - New Insight into Solubility Levels and Reaction Mechanisms

“…If drilling waste that contains precipitated barium carbonate is discharged to the ocean, the barium will immediately recombine with sulfate as barium sulfate is extremely insoluble in water. For comparison the typical concentrations of soluble barium in produced waters from HPHT gas reservoirs that are discharged to the North Sea are in the 1,000 -3,000 mg/L range [Wat, 2008]. In other parts of the world, levels as concentrations of soluble barium as high as 13,000 mg/L have been reported [Silva, 2012].…”

Downhole Chemical Injection Lines - Why Do They Fail? Experiences, Challenges and Application of New Test Methods

“…The scale prevention strategy for a HPHT field was continuous injection of scale inhibitor upstream the downhole safety valve. A severe calcium carbonate scaling potential was identified in the well (Wat et al 2008). One of the challenges was high temperature and high gas and condensate production rates combined with low water production rate.…”

Scale Inhibitor Application in Northern Alberta: A Case History of an Ultra High Temperature Scale Inhibition Solution in Fire Tube Heater Treaters

“…Other previous studies in the literature are largely focused around downhole scale inhibitor squeeze applications covering temperatures upward of 150°C but rarely above 200°C (e.g. Graham et al, 2002;Wylde et al, 2003;Wat et al, 2008). One study, that resulted in a patent, describes scale inhibition in geothermal wells up to 370°C (Lawrence et al, 1991) using an acrylate/acrylamide scale inhibitor but no field application details are available.…”