Field Hydraulic Tests Improve HPHT Drillng Safety and Performance

Abstract

Abstract For the Elgin-Franklin UKCS fields, drilling of the HPHT phase is critical due to the narrow margin between formation pore and fracturation pressures. This problem is accentuated by the extreme temperature (up to 205C - 400F) and pressure (up to 1200 bar - 17400 psi). A new generation of down-hole Pressure While Drilling (PWD) tools allows a better real-time monitoring of the bottom-hole pressure, but cannot withstand the extreme temperature of the entire HPHT phase. Furthermore, down-hole and surface pressures are dependent on complex hydraulic phenomena which make predictions challenging. Consequently it was decided to perform hydraulic tests before drilling the HPHT section of the well 22/3Oc-G4 (first Elgin development well), in order to quantify the surface and down-hole pressures and temperatures on several operating conditions: circulating (with an without pipe rotation), tripping and flow check. Gelation tests, trapped pressure as well as pressure transmission tests were also performed. Objectives of these tests were: to better understand some complex down-hole physical phenomena, to prepare practical guidelines (such as mud density variations, Equivalent Static Density values, ECD function of flow rate and pipe rotation, mud compressibility values, tripping procedures, etc…) before drilling HPHT sections, to check reliability and accuracy of new Real Time PWD tools, and to collect accurate well data for further hydraulic software packages validation or improvement. These procedures led to great benefits, both in terms of safety and performance, when drilling the HPHT phases of the well: results were considered as highly positive. This paper details down-hole measurement procedures and results, operational guide lines, tools performances, lessons learnt, and explain how to cope with sources of possible discrepancies between actual values and software predictions. P. 551