Design and Development of an HPHT Drillstem Testing Valve: A Case Study in HPHT Tool Design

Abstract

The past several decades have shown a steady trend of work performed in increasing well temperatures and pressures; however, the industry has been slow to adopt new methods in the design of equipment to be used for these wells. As a result, certain types of equipment are now insufficient for operations in high-pressure, high-temperature (HPHT) wells. This hinders the development of HPHT fields and reduces the ultimate recovery from those fields; technologies that are successfully used in conventional wells are only very reluctantly used in HPHT wells.Drillstem Testing (DST) valves are used for DST work, but also for tubing-conveyed-perforating (TCP) "shoot and pull" operations. These valves enable under-and over-balanced perforating, increasing the perforation quality and minimize the formation damage caused by kill fluids. However, these types of valves are frequently perceived as insufficiently reliable for TCP operations in HPHT wells, and frequently simpler perforation jobs are performed, sacrificing perforation performance for reliability.A new DST Combined Test tool was designed with advanced analysis methods. These methods include not just stress and deflection analysis, but also an analysis of historic failure modes, including human factors, and the implementation of mechanical fail safes to prevent them in the new valve. The valve was tested to 30,000 psi hydrostatic with tubing pressure in excess of 40,000 psi, and at 400°F. Finally, the valve has been successfully deployed on field trials. This paper will present an overview of the valve development as a case study for the development of future HPHT tools.