Unconventional Approaches for the Unconventional Resources in Central China

摘要

Operators began evaluating the shale gas block in Central China since Dec 2010.During their exploration and appraisal phases,3 horizontal wells were drilled.Their challenges consisted of hard,abrasive formations with kicks,losses,stuck pipe and over pressure.The problems were amplified by high geological formation dip,faults,and stratigraphic uncertainties.As a result,they were unable to achieve efficient drilling using conventional motor bottom hole assembly(BHA),that made it difficult to run casing,and multiple geological side-tracks were the norm.Naturally,these wells exceeded authorization for expenditure(AFE)curves,requiring an average duration of 200 days per well. This paper features the challenges and lessons learned along with the unconventional approaches that were employed to address these challenges.Four key categories of the process were identified: They consisted of emerging technologies such as a hybrid and robust rotary steerable system(RSS),real time rate of penetration(ROP)optimization and high resolution real time logging while drilling(LWD)image data tools.In addition, drilling and best practices adopted were managed pressure drilling(MPD),high dog-leg-severity(DLS)curve with smoother borehole,and low cost rotating blowout preventer(BOP)with higher revolution per minute(RPM).In the absence of 3-D seismic data,2-D seismic data combined with LWD data were used.Integrated Operations&Innovative Commercial Contract with local drilling service contractors had made a big impact in terms of faster well delivery and overall cost saving.Another step change was with the performance based commercial contract that helped to attain the ultimate goal to meet health,safety and environment(HSE)and time requirements. At the end of 2013,11 horizontal wells were drilled and completed.Amongst these,one well was categorized as Top Quartile and four were Best-In-Class.Additional highlights include significantly reduced geological side-track;quadruple footage drilled per day and the reduction in drilling cost.Average well duration was significantly cut to 110 days. These accomplishments consequently enhanced the drilling schedule sequence with longer horizontal wells being planned and greater confidence of predictability and repeatability. The paper will conclude with a summary of comparative learning statistics.The team believes that this is a big step towards delivering Best-In-Class wells in complex geological structure.The next step is to realize the ambition of factory drilling at a further reduced cost to tap the unconventional plays in the Sichuan basin,and bring cleaner fuel to Central China as a replacement of coal.