As the search for oil & gas leads to deeper reservoirs, extreme pressures and temperatures have become key considerations in reservoir development. New and innovative technologies are being developed to meet the challenges of evaluating and completing HP-HT wells and bringing these fields on-stream.
In oilfield, wells with bottomhole pressure more than 10,000 psi and bottomhole temperature in excess of 300°F are considered as HP-HT and wells with bottomhole temp in excess of 350°F are considered extreme HP-HT environment. Testing of such extreme HP-HT wells require special testing equipment that can sustain the high pressures and temperatures.
The paper presents case history of an extreme HP-HT well, Qadirpur Deep-1, by Oil & Gas Development Co. Ltd (OGDCL) the national company of Pakistan including the planning, design phase, implementation, data interpretation and lessons learned from successful testing operation (BHP = 13,500 psi, BHT = 377°F and WHP = 10,800 psi). The lessons learned and conclusions made will be helpful in future development and optimization of the new discovered field and other similar HP-HT wells.
Qadirpur deep-1 (QP D1) was drilled in 2006 by OGDCL. The well is located in Sindh province in the South of Pakistan.
The well was drilled to a total depth of 4703 m, and 5" liner was set from 4018 to 4675 m. Due to complications the 28 m of CHILTAN formation was left as open hole. During drilling a strong gas kick was experienced and 12,000 psi gas pressure was recorded at surface during circulation.
Since, the well was rated as highest HP-HT in Pakistan (expected BHT = 380°F) it was a challenging task and new experience for OGDCL to successfully test such a well. The complications and recorded pressure experienced while drilling generated a number of constraints that had to taken in the planning and preparation of such an extreme HPHT testing. Since no MDT was carried out so results of DST were highly anticipated.
Schlumberger was asked for the testing of QP D1, which included three slimhole drill stem tests (DST), (G-String 3-1/8" OD, 1- 1/8" ID Schlumberger DST tools designed for slimhole 5", 4-1/2" liners or casings) and HP-HT gauges for the BHP & BHT measurements. Perforation was planned to be done with SLB WL with overbalance. As the expected BHP was 13,000 psi, BHT = 380°, and WHP was expected to be 12,000 + psi, dry gas production, so this required the use of special 15k surface equipment which was not available in the country and required certain mobilization period. Reviewing the hostile conditions of the well the testing of QP D1 was hence delayed with an intention to plan the testing program in detail prior to remobilizing the rig.
More than twelve months of extensive planning and preparation was done for the special equipment required for the testing of QP D # 01. Special attention and collaboration was done between OGDCL and other companies for HSE issues to eliminate any risks while still achieving the required test objectives.
The design was approved through Schlumberger in Touch support supported by professionals and permission was given to use Gstring tools and WTSR gauges at high temperature of 380+ °F on OGDCL special request for the job (Note: G-String rated @ 375°F and WTSR gauges rated @ 374°F).