Uranium Wells: The Proper Selection of Drilling Mud and Completion Fluid Has Changed All the Rules of the Game

Abstract

In Southern Kazakhstan, uranium ore is produced by the in-situ leaching (ISL) method. One of the uranium companies, which is producing in this manner experienced difficulties in attempting to increase yield when using bentonite-polymer mud and sodium hypochlorite for removing the filter cake. The company had additional objectives that included increased production cycle time and optimization of drilling technology to reduce well construction time.The design of a typical well is represented by a vertical shaft 215.9 mm in diameter and up to 500 m deep. The well is cased by plastic pipes with a filter lining in the pay zone interval. Bottomhole temperature is in the 25-28°C range.A three-stage concept has been proposed to complete these tasks: the use of inhibiting polyacrylamide (PAA)-based mud on the upper nonproductive intervals and a specialized mud system designed for completion of productive horizons, which includes only acid-soluble and biodegradable components. The final stage involves treating the reservoir with a filter cake removal system. Instead of sodium hypochlorite, an organic product has been proposed for the removal of the filter cake, exhibiting many advantages, such as increasing the reaction time for acid formation, deep penetration into the near-wellbore region, and guaranteed treatment of the entire interval, unlike conventional acids, which react instantaneously and are; therefore, inefficient in horizontal intervals.These technologies were successfully applied and have provided a number of benefits to the customer, including an increase in well productivity by 20% as compared to the adjacent wells and up to a 10-fold yield increase in wells with depleted reservoirs. Time to reaching the design yield decreased on average by 30% while reducing the total well commissioning time by an average of 10%.This article introduces some aspects of these technologies and the results of their application.