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.
Low cost, high technology and fast ROP are three main factors which related to successful development of unconventional shale gas all over the world. Local operator and international operator are using different approaches to develop shale gas in Sichuan basin, where is a hot place for shale gas chasers in China. Both operators have some filed application lesson learnt to improve drilling efficiency and save cost during past 3 years:Flexible local well structure optimization design reduces loss risk.Local factory drill is proven to improve working efficiency and reduce cost per well.Local service providers help to reduce cost, especially, local DD/MWD/LWD service.Local Well placement concept reduces downhole collapse issue through filed application lesson learnt.New push to bit and point to bit combination tool has high efficiency to improve ROP, especially, in curve section.Near bit gamma ray/Gamma ray image is a useful tool for high dip angle / multi-faults formation horizontal section well placement, to avoid geological sidetrack.Bit optimization helps to improve ROP and extend downhole working life. Through above filed applications, average cost of international operator is 1.7 times of local operator, but on bottom ROP is 1.5 times faster than local operator. Both operators' drilling efficiency has average 70% improve which based on previous 3 years learning curves. Local operator tries to factory drill 6 wells per pad with 300m well spacing and 8 wells per pad with 400/500m well spacing separately next step and find the best well placement to improve production in Sichuan basin. The production target of unconventional shale gas will be attempted to 600-1000 X 108 m3 per year until 2020.
Being the world's third largest shale gas producer after the US and Canada, China delivered an output of 9 billion cubic meters (bcm) in 2017. China has the world's largest technically recoverable reserves of shale gas, of which US Energy Information Administration (EIA) estimates at 31.6 tcm, 68% higher than shale reserves in the US. Unlike the US who started to explore shale gas in the 1980s, China only completed the first shale gas well in 2011. Development of shale gas resources is expected to play a vital role in China's enthusiastically planned transition to a low-carbon energy future. On September 14th, 2016, Chinese National Energy Board released Shale Gas Development Plan 2016-2020. In the plan, shale gas production goal was set at 30 bcm for 2020. With an average shale gas production of 20MCM per well per year, it is estimated that a minimum of 1500 horizontal wells with 1000m lateral length are needed by the year of 2020. The question arises whether what kind of drilling performance is needed to meet the aggressive development target. In less than a decade, Petro China, its subsidiaries and contractors have made significant breakthroughs in shale gas exploration, not only in capacity, but also drilling techniques. The paper captures the success and lessons that the drillers had gained in the last 7 years in terms of drilling performance. It is well known that China shale gas reserves are in geologically challenging areas. The challenges consisted of hard formations with kicks, losses, frequent stuck pipe and over pressure formation. The problems were amplified by high geological formation dip, faults, and stratigraphic uncertainties. In this harsh drilling environment, rate of penetration was slow, trajectory control is difficult, mud weight and circulating pressure are high, downhole torsional vibration, drilling torque and stick&slip are high, rig equipment and downhole tools fail prematurely, and non-productive time is excessive. Over the years, the team had demonstrated that with systematic, scientific and engineering drilling approaches, a considerable improvement in drilling performance can be achieved. To deliver and execute the optimized drilling approaches, high intregration and synergy between each drilling segment are required. These approaches are nothing new in the drilling world, these are optimization in Well Plan, Mud Properties, Rig Capacity & Drilling Parameters, Bottome Hole Aseembly (BHA) selection and design, best Drilling Practice and Drilling Operation Efficiency. These are all part of a formula to success; the key is to rightly balance each one of them. The team sucessfully reduce average well days from 120 to 30 in one particular field. Along the way, the team also identify a few more components to the formula of success, with that, the short-term goal shall be further reducing the well days to 25 days, and less than 20 days in long term.
Changning shale gas block is located in the southern part of the Sichuan basin. It is one of the first pilot experimental shale gas blocks in China. The paper will elaborate the drilling challenges in the field and the overall drilling performance with conventional approaches. In 2014, new drilling tools and methods were tried and applied. These significantly improved the performance, further elevating the drilling speed to a new level.The paper will review the drilling performance of horizontal wells completed previously in the field. It will focus on demonstrating formation characteristics, well trajectory and geometry design, drill bit and directional bottomhole assembly (BHA). One of the biggest challenges is the hard rock on top of the shale formation that constrains the drilling speed, especially when designing the curve interval at the hard rock. By analyzing the drilling challenges, a new drilling system and method were introduced to the project in 2014 to combat the challenges. It has been proven successfully with actual drilling data.Initially, as a pilot project, conventional motor technology was applied to six horizontal wells in Changning block. The average well drilling cycle was approximately 66 days for 1000 m of lateral section. The main challenge with motor drilling was high drag at the curve and lateral due to extreme friction as high mud weight was applied to balance the formation stability. This resulted in a poor on-bottom penetration rate during sliding mode. Directional work at the hard rock formation posed an additional challenge. In early 2014, a hybrid high-build-rate rotary system was applied to deepen the kickoff point and avoid the steering work in the hard zone. Air drilling was used to drill vertically across the hard rock. A power rotary steering system was also implemented to further improve the drilling speed in the lateral section. The combination of technical approaches led to significant drilling improvement. The rate of penetration (ROP) on bottom at the curve section has improved 200% over conventional drilling. The well drilling cycle was cut in half, which was considered as a breakthrough achievement in the field.With the application of hybrid high-build-rate rotary steering system, the new well design can be executed. Air drilling is chosen to drill through the hard rock in the shortest distance. Using the power rotary steering system for the lateral further promotes the drilling performance to a new level.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.