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Shale gas is defined as natural gas occurring in shale formations. It is an unconventional energy resource, which has become an increasingly important source of natural gas globally and has the potential to grow as a major energy source in the next decade. However, production of shale gas remains technically and economically challenging. Having high total organic content and falling in the gas window (302 F–392 F), shale has sufficient potential to generate huge amounts of natural gas. Generally, natural gas is stored in a shale matrix, which is highly porous but has very poor permeability.
Qian, Jialin (School of Chemical Engineering, China University of Petroleum Beijing, China) | Wang, Jianqiu (School of Chemical Engineering, China University of Petroleum Beijing, China) | Li, Shuyuan (School of Chemical Engineering, China University of Petroleum Beijing, China)
Summary Drilling activity has increased dramatically in unconventional shale gas reservoirs. The drilling fluid of choice in these shale plays is often nonaqueous-based fluid (NAF). While NAFs can provide advantages such as shale stabilization, lubricity, and contamination tolerance, environmental consequences and associated costs are an issue. These disadvantages cause operators to seek water-based muds (WBMs) for drilling many of these gas reservoirs. Despite some operational similarities, a wide variety of unique downhole conditions can be found in the shale plays. Shale mineralogy and bottomhole temperature (BHT) represent just two highly variable critical factors in unconventional gas reservoirs. Therefore, a single water-based solution for addressing shale plays globally is not a realistic option. Instead, a customized approach that delivers WBMs formulated specifically for a given shale play has been pursued. Customization relies on detailed analysis of the well parameters of a given shale play. This analysis includes not only the shale morphology and lithology but also well drilling program plans, environmental factors, and other reservoir-specific considerations. Applying appropriate drilling-fluid chemistries on the basis of this detailed analysis has led to the successful field deployment of a number of new shale fluids. Details of the process used for customizing a WBM for a shale play, as well as specific examples of new fluids developed for the Barnett, Fayetteville, and Haynesville shales, are presented in this paper. Full laboratory development and testing are described. Additionally, field-trial results are presented that show that specially designed WBMs can provide performance comparable to that of NAFs, but with enhanced environmental and economic benefits. Application of the customization process to develop WBMs for other shale plays around the globe is also discussed.
Abstract With the depletion of conventional fossil resources and growing demand for energy, unconventional energy is playing a more important role in the world energy market. Nowadays, unconventional gas production contributes to around 50% of total gas output in the USA Shale gas has significantly changed the energy portfolio in the USA and reduced America's dependence on oil and gas imports. The case histories of four major shale gas plays in the USA, Antrim, Barnett, Haynesville, and Marcellus, are discussed in this paper. It is concluded that the phenomenal shale gas success in the USA benefitted from improved horizontal drilling and fracturing technology, positive government policy and tax incentives, and mature surface pipeline system. China is facing with soaring energy demand and the pressure to cut greenhouse gas emission. These factors have motivated oil operators to explore and exploit the enormous shale gas resources in China, especially in the Sichuan and Tarim Basins. But several factors may hinder the future of shale gas in China. Firstly, Chinese operators have to develop suitable drilling and fracturing technologies. Secondly, lack of water resources may restrain fracturing operations. Thirdly, China lacks mature pipeline system. Fourthly, the Chinese national oil companies may not be interested in producing shale gas due to its low price and low profits. Therefore, it is emergent for the Chinese government to invest in innovations and infrastructure, and allow independent and private companies to engage in the shale gas business.