Alternate Weighting Material for High Pressured Jurassic Wells in Kuwait - Case Histories of Successful K-Formate Mn3O4 Drilling Fluids

Abstract

Abstract Deep wells drilled into the Jurassic formations of Kuwait have long utilized oil based mud (OBM) with barite as the weighting material. However, barite caused considerable damage to the reservoir sections, resulting in reduced production rates. The high oil content in the OBM also prevented recording of good quality image logs, which was necessary to identify the micro-fractures in the reservoir. To overcome these issues, it was necessary to use a water based mud (WBM) with non-damaging weighting material suitable for high pressure conditions. The existence of high pore pressures and a requirement for mud weights up to 18.5 lb/gal in these wells ruled out the use of conventional WBM. Laboratory tests conducted using a fluid based on Potassium Formate (K-Formate) brine weighted with Manganese Tetraoxide (Mn3O4) as an alternate weighting material. This fluid was successfully applied in a number of deep wells, resulting in increased production rates, up to three times higher than the wells drilled with OBM. Damage to the reservoir was considerably reduced as the wells were easily activated. High quality image logs were also recorded which was not previously possible with OBM. K-Formate-Mn3O4 fluid is a non-corrosive, biodegradable, environmentally friendly fluid, capable of long term storage without degradation of mud properties and recyclable, which reduces fluid cost in subsequent wells. This paper will review the case histories of twelve deep exploratory wells where the K-Formate-Mn3O4 fluid was applied successfully. Issues including, high rheology encountered while increasing the mud weight using Mn3O4, fluid related complications in drilling and solutions developed to overcome the problems will be discussed in detail. Lessons learned in each deep high pressured well, mud loss scenarios and well control issues will be discussed. K-Formate-Mn3O4 based drilling fluid has been highly successful in drilling high pressured Jurassic reservoirs in Kuwait. Following the success of the fluid in these wells, it is now being planned to apply in all future deep exploratory wells.