|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Journal Paper|
|Title||Field Hydraulic Tests Improve HPHT Drilling Safety and Performance|
|Authors||Patrick Isambourg, D.L. Bertin, Elf Exploration Production; Martial Brangetto, Elf Exploration UK plc|
|Journal||SPE Drilling & Completion|
|Volume||Volume 14, Number 4||Pages||219-227|
|Copyright||Copyright 1999. Society of Petroleum Engineers|
For the Elgin–Franklin UKCS fields, drilling of the high pressure/high temperature (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 205°C—400°F) and pressure (up to 1,200 bar—17,400 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 22/30c-G4 (first Elgin development well), in order to quantify the surface and down-hole pressures and temperatures on several operating conditions: circulating (with and 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, 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 explains how to cope with sources of possible discrepancies between actual values and software predictions.
When drilling the HPHT section of the Elgin–Franklin wells, we must cope with the very narrow margin between the formation pore and fracturation pressures. Therefore it is necessary to maintain the down-hole mud pressure inside this “safe operating window,” in order to avoid any kick or losses problems, which could have drastic consequences due to the very high gas pressure. Prediction of this pressure is very challenging because of the numerous phenomena that influence this value:
The stand pipe pressure (SPP) cannot be used to monitor the bottom-hole pressure because it is mostly dependent on the pressure losses inside the drill string assembly, but could be used to monitor the down-hole rheological behavior of the mud.12 Nevertheless the down-hole pressure must be calculated from ?es and annular pressure losses, and is still dependent on accuracy of hydraulic formula and geometrical data.
Down-hole memory gauges help to quantify dynamic pressure and temperature, 13 and to construct flow charts, but it is impossible to monitor the down-hole pressure in real-time.
Development of a new generation of pressure while drilling tools allows the monitoring of the bottom-hole pressure and the optimization of drilling practice,14-16 but they have still temperature and pressure limitations (175°C, 20,000 psi). Therefore it is necessary to check the real-time pressure while drilling (RTPWD) tool reliability at high temperature conditions with a heavy mud (2170 kg/m3), in order to decide if we can use it, with confidence, to optimize parameters while drilling the HPHT section. Moreover, PWD tools cannot send measurements to surface in static or tripping conditions, thus, software predictions are still necessary in these conditions, as well as in operation planning.
For these reasons, Elf Exploration UK decided to conduct “hydraulic tests” before drilling the HPHT section of well 22/30c-G4.
The primary goals of these tests were to define operational guidelines for drilling the HPHT section, and to check reliability and accuracy of the real-time PWD tool. The additional goals were to collect data to better understand some complex down-hole hydraulic phenomena, as well as to further validate and improve software packages. The test program was successfully carried out within the rig-time allocated, and the quality of data collected was very high.
This paper focuses on surface and down-hole measurements, on operational guidelines, and discusses briefly the source of discrepancies between measured and predicted values.
Well Specifications and Test Program
|File Size||419 KB||9|