Technologies in Discovery and Exploration of Fuling Shale Gas Field, China

Abstract

Marine shale gas in South China is widely distributed and demonstrates an enriched resource. Compared with the North American commercial shale gas field, the shale formation in South China is featured by old age, multiple stages tectonic movements, and high thermal evolution degree and complex reservoir forming conditions. As a result, the existing theories and technical methods of exploration in North America cannot be simply applied to South China. Since 2007, based on the in-depth study on a large quantity of analytical test data, we have conducted the theory and technology research for the southern marine shale gas, found Wufeng-Longmaxi Group deep water shelf high-quality shale gas critical parameters coupling laws, proposed the "Binary Enrichment" theory for highly evolved marine shale gas in southern complex tectonic zone, and established a zone selection and evaluation criteria, which are based on the quality of shale, for the key of preservation condition, and for the purpose of economy. Taking this as a guide, we selected Longmaxi formation Lower Silurian of Fuling area in southeastern Sichuan Province as the preferred breakthrough field for the shale gas exploration. The Jiaoye 1 well has the daily gas production of 20.3 × 10 4 m 3 , which embarked the found of China's first large-scale business development gas field, the Fuling shale gas field. And we submit the first domestic shale gas proven reserves of 1067.5 × 10 8 m 3. The Fuling shale gas reservoirs are deep water shelf marine high-quality shale, with favorable thickness and even distribution, without dissection in the middle. They are typical self-generation and self-storage shale gas reservoirs. The gas fields have high production gas well; high pressure gas reservoir, good gas components and good exploit results, and there for the Fuling shale gas field is characterized by mid-depth, high pressure, high reservoir pressure, and high quality gas accumulation. Up to March 24, 2014, all of the 101 fracture-gas testing wells have obtained middle and upper shale airflow, with the average single well test production of 32.6 × 10 4 m 3 /d. In the exploration and development process, technology series in geological evaluation, horizontal well, drilling, well completion, piecewise fracturing techniques have been gradually formed. It is of great importance to commercially develop the domestic shale gas and promote the restructuring of China's energy structure.

Approaches for the evaluation of favorable shale gas areas and applications: Implications for China's exploration strategy

“…11,13 The Cengong Block is considered as a relatively favorable area for shale gas accumulation of the Lower Cambrian Niutitang Formation in northern Guizhou, but it is important to note that the organic matter has a high thermal maturity despite the advantageous shale gas geological conditions, 24 and the results of this study are consistent with those made previously. 11,13 The Cengong Block is considered as a relatively favorable area for shale gas accumulation of the Lower Cambrian Niutitang Formation in northern Guizhou, but it is important to note that the organic matter has a high thermal maturity despite the advantageous shale gas geological conditions, 24 and the results of this study are consistent with those made previously.…”

“…In the early stages of China's shale gas exploration, the Jiaoshiba Block was chosen as a Class I target area of the Lower Silurian Wufeng-Longmaxi Formation in Fuling area because of the simple structural conditions and favorable sedimentary environment. 11,13 The Cengong Block is considered as a relatively favorable area for shale gas accumulation of the Lower Cambrian Niutitang Formation in northern Guizhou, but it is important to note that the organic matter has a high thermal maturity despite the advantageous shale gas geological conditions, 24 and the results of this study are consistent with those made previously. The rationality of the evaluation results is also proved by exploration and development practices.…”

“…In the entropy method, the indexes with higher weight values are quite distinct from the others and make a significant difference in the ranking outcomes of the evaluation object. Additionally, the factors serving as the key indexes for shale gas favorable area evaluation, such as TOC, shale thickness, Ro, burial depth, and gas content, possess higher weight values because China's shale gas selection area, 11 at the present stage, mainly focuses on the optimization of shale gas geological conditions, which is consistent with the previous standard evaluation workflow for unconventional shale gas. Nevertheless, there is a weak correlation between λ GRA and both λ AHP and λ EWM , having R 2 = 0.1694, θ = 0.7140; and R 2 = 0.0468, θ = 0.7385, respectively.…”

“…F I G U R E 7 Influence of the resolution coefficient ρ (A) and chosen mother factor (B) on the index weights calculated using the gray correlation method On the basis of the above discussion, combinative weights (λ C ) were calculated using λ AHP and λ EW and Equation (10), which combines the subjective and objective approaches, surface and underground factors, geological and economic conditions, hierarchical and logical structure, and quantitative and qualitative indexes (Figure 8). Additionally, the factors serving as the key indexes for shale gas favorable area evaluation, such as TOC, shale thickness, Ro, burial depth, and gas content, possess higher weight values because China's shale gas selection area, 11 at the present stage, mainly focuses on the optimization of shale gas geological conditions, which is consistent with the previous standard evaluation workflow for unconventional shale gas. 20,56 Compared with the previous works aimed at shale gas development, market conditions possess lower weigh values in this work, and the reference 44 in which the weigh values calculated by AHP presented the relevant information.…”

“…The degree of consistency of the weight calculation results obtained using various methods was assessed using the coefficient of determination, R 2 (0 ≤ R 2 ≤ 1), for the two different approaches and the angle, θ (0 ≤ θ ≤ 0.7854, unit: radians), between the fitted line and the y = x line. 32 The EDM, which is similar to the entropy approach, determines the weights of the indexes in terms of their variability via Equations (11) and (12). Among the weight calculation approaches mentioned in this study, the AHP is commonly considered to be a subjective decision-making method, not only because of numerous qualitative factors but also because of the discrete scale used to handle the uncertainty and ambiguity in deciding the factor attribute characteristics of the comparison matrix.…”