Fuling Shale Gas Research Articles

A quantitative seismic prediction technique for the brittleness index of shale in the Jiaoshiba Block, Fuling shale gas field in the Sichuan Basin

In this paper, a quantitative seismic prediction technique of multi-parameter shale brittleness index suitable for the environment with complex structural stress was developed in order to confirm highly brittle intervals and favorable fracturing zones in the shale reservoirs in the Jiaoshiba Block, Fuling shale gas field, Sichuan Basin. Firstly, the effect of structural compression stress on the brittleness characteristics of rocks were figured out by analyzing structures, mineral composition, development degree of fractures in cores, well logging and seismic data comprehensively. Secondly, according to the Rickman formula, a new brittleness index prediction model based on Young's modulus, Poisson's ratio and shear modulus × density was established by introducing the shear modulus which reflects lateral shear stress–strain. Finally, the quantitative prediction technique of multi-parameter shale brittleness index suitable for the environment with complex structural stress was developed by virtue of the superiority of an elastic rock brittleness index method based on mineral composition to accurately calculate the brittleness index of a full hole. Field application shows that this technique is reliable, since its prediction results coincide with the calculated brittleness index of exploratory wells which are not used for modeling, with a relative error margin below 4%; and that the brittleness index of good shale of Upper Ordovician Wufeng Fm–Lower Silurian Longmaxi Fm in the Jiaoshiba Block increases from the top to the bottom and is stably distributed laterally. Particularly, the Wufeng–Longmaxi 11 is the highest in brittleness index, so it is the most favorable interval for penetrating and fracturing of horizontal wells.

Preservation mechanism of Fuling shale gas

Preservation mechanism of Fuling shale gas

Distinguishing kerogen and oil cracked shale gas using H, C-isotopic fractionation of alkane gases

The formation mechanism of 23 shale gas samples from the Fuling shale gas field in the Upper Ordovician Wufeng (O3w) Formation-Lower Silurian Longmaxi (S1l) Formation marine shales was investigated based on the carbon and hydrogen isotopes of methane, ethane, and propane. Fuling shale gas is mainly composed of alkane gases, and has a dryness coefficient, C1/C1-3, of 0.992–0.993. The reversed carbon isotopic trend where δ13C1 > δ13C2 is a typical characteristic indicating mixing of kerogen cracked gas and crude oil cracked gas. The empirical correlations between ln (C1/C2) vs. ln (C2/C3) and ln (C1/C2) vs. δ13C of alkane gases at different thermal maturity levels were used to distinguish kerogen cracked gas from crude oil cracked gas. Five stages of kerogen cracking and crude oil cracking were identified with a wide range of thermal maturities (vitrinite reflectance %Ro): 1) %Ro < 0.8: shale gas showed a normal isotopic trend (δ13C1 < δ13C2) and was dominated by primary kerogen cracking; 2) %Ro of 0.8–1.5: primary kerogen cracking ended, and crude oil cracking was initiated, which is associated with a normal isotopic trend of methane and ethane (δ13C1 < δ13C2); 3) %Ro of 1.5–1.8: the gas is the mixture of gases from both late kerogen cracking and oil cracking, with an initially reversed carbon isotopic trend of δ13C1 > δ13C2; 4) %Ro of 1.8–2.5: residual kerogen cracking proceeded to generate CH4, and light oil cracking generated heavier gaseous hydrocarbons, with a completely reversed carbon isotopic trend of alkane gases (δ13C1 > δ13C2 > δ13C3); 5) %Ro > 2.5: further cracking of heavier gaseous hydrocarbons generated CH4.

The Application of a New Neutron Induced Gamma Ray Spectroscopy Tool in Evaluation the Shale Gas in Fuling Shale Gas Field

Shale gas reservoir is characterized by complex lithology with ultra-low porosity and permeability, which brings many challenges in the formation evaluation. Elemental Capture Spectroscopy Sonde (ECS) can be used to measure the elements and get the formation of the mineralogy. LithoScanner is a newly-generated spectroscopy tool, which can be used to measure both inelastic and capture spectra, providing estimation of more elements, including silicon, calcium, iron, sulfur, titanium, gadolinium, aluminum, potassium, sodium, magnesium, manganese, carbon, etc. LithoScanner can be directly used to measure the total organic carbon content (TOC) in the formation, and provide solutions to the lithology classification and heterogeneous rock analysis (HRA). The changing lithology and borehole rugosity have little influence on the direct measurement of TOC by LithoScanner. LithoScanner shows great advantage in accuracy when comparing with other methods using triple-combo. The systematic lithology classification method in shale gas reservoir using LithoScanner is correlatable in multi-wells. The brittleness index from mineralogy can be applied to hydraulic stimulation. HRA results offered guides in both the coring sample selection and the experiment. The advantages of LithoScanner in shale gas formation evaluation were presented in this paper, and the workflow can also be applied to other reservoirs.

Assessment of Methods for Forecasting Shale Gas Supply in China Based on Economic Considerations

Shale gas, with its lower carbon content and pollution potential, is the most promising natural gas resource in China. When modeling the shale gas supply in a specific gas field, it is of paramount importance to determine the gas supply under economic considerations. Two common calculation methods are used in China for this purpose: Method 1 (M1) is the breakeven analysis, where the gas supply is based on the relationship between costs and revenues, while Method 2 (M2) is the Geologic Resource Supply-Demand Model, where the supply relies on demand and price scenarios. No comparisons has been made between these two methods. In this study, the Fuling shale gas field in the Sichuan Basin was chosen as a study case to forecast the shale gas supply using these two different methods. A sensitivity analysis was performed to discuss the influencing factors of each method and error measures were used to compare the different shale gas supply values calculated by each method. The results shows that M1 is more sensitive to initial production, while M2 is more sensitive to gas price. In addition, M2 is more feasible for its simplicity and accuracy at high price scenarios and M1 is considered to be reliable for low price scenarios with profit. This study can provide a quick and comprehensive assessment method for the shale gas supply in China.

Geological factors controlling shale gas enrichment and high production in Fuling shale gas field

Abstract Based on the understandings on enrichment rules of marine shale gas in southern China and data obtained from exploration and development in Fuling shale gas field, this article discusses the key controlling factors on shale gas enrichment and their relationships, it also discusses further the theory of Two-Factor Enrichment of marine shale gas in southern China. The bases for shale gas enrichment are shale gas generation and accumulation, the shale gas reservoirs of deep-water shelf are characterized by high TOC, high porosity, high gas contents and high siliceous contents, with high hydrocarbon-generation intensity. The organic pores are rich in shales in favorable for stimulation, so they are the bases for large scale hydrocarbon accumulation. Preservation conditions are vital to the formation and enrichment of shale gas reservoirs, good top and base layers can effectively prevent hydrocarbon from escaping vertically at the beginning of hydrocarbon generation. Shale gas preservation conditions depend on the intensity and duration of tectonic movements, good preservation conditions are key geological factors for shale gas accumulation, shale reservoirs have high gas contents, high porosity and high pressure and are likely to form high yield area of shale gas.

Elemental geochemistry of lower Silurian Longmaxi shale in southeast Sichuan Basin, South China: Constraints for Paleoenvironment

A significant proportion of shale gas resources occurs in Lower Silurian Longmaxi Formation in southeast Sichuan Basin, South China, where commercial gas production has been achieved at Fuling Shale Gas Field. This study area is located adjacent to Fuling Jiaoshiba shale play. Elemental geochemistry regarding paleoenvironment aspects of lower Silurian Longmaxi shale gas is poorly understood. However, the samples in this study are representative, revealing the complete elemental geochemical characteristics of Longmaxi Shale. This research has analysed trace and rare earth elements of lower Silurian Longmaxi Shale and investigated the depositional environment, provenance, and tectonic settings when this type of shale formed. Sedimentary structures include horizontal lamination, massive lamination, and deformation structures that are well developed in black shale and grey silty shale of lower Silurian Longmaxi Formation. Gamma ray, total organic carbon, and pyrite contents are relatively higher in the lower part of the shale. The enrichment of sulfophile heavy metal elements (Cu, Zn, Pb, Mo, Ni) indicates that a reducing environment is common during the deposition of Longmaxi Formation. The concentration of rare earth elements is generally constant with relatively high concentration of light rare earth elements, stable concentration of heavy rare earth elements, and negative Eu anomalies. The sediments of Longmaxi Formation are derived primarily from the sedimentary rocks and granites in continental crust. The combination of trace and rare earth elements indicates that the tectonic settings of the provenance are continental island arc and active continental margin.

A study on the oil-based drilling cutting pyrolysis residue resource utilization by the exploration and development of shale gas.

Based on the requirement of national energy conservation and environmental protection, attention has been given to building an environment-friendly and resource-saving society. Shale gas oil-based drilling cutting pyrolysis residues (ODPRs) have been used as the main research object to developing new technology which can convert the residues into a harmless and recyclable material. Using the test data of ODPR, we analyze the development prospect in the building material industry and provide a scheme to utilize this particular solid-waste efficiently. Theoretically speaking, the ODPR resource utilization such as admixture of cement, making sintered brick, and non-fired brick, by the exploration and development of Fuling shale gas is feasible.

The application of geostatistical inversion in shale lithofacies prediction: a case study of the Lower Silurian Longmaxi marine shale in Fuling area in the southeast Sichuan Basin, China

Based on cores, well logs and seismic data, we established the isochronous sequence stratigraphic framework of the Lower Silurian Longmaxi Formation and predicted the shale lithofacies distribution within the sequence stratigraphic framework using geostatistical inversion. The results of our study show that the Lower Member of the Longmaxi Formation is a third order sequence that includes a transgressive systems tract (TST), an early highstand systems tract (EHST) and a late highstand systems tract (LHST). Four lithofacies units have been recognized, specifically siliceous shale, argillaceous shale, calcareous shale and mixed shale. The results of geostatistical inversion reveal that the TST is characterized by flaky siliceous shale and some sparsely distributed calcareous shale. The EHST is dominated by mixed shale with minor amounts of siliceous shale, which occurs in only a small area. Moreover, in the LHST, argillaceous shale occupies almost the entire study region. Comparing to traditional geological research with geophysical research, the vertical resolution of the predictive results of geostatistical inversion could reach 1–2 m. Geostatistical inversion effectively solves the problem of precisely identifying the lithofacies in the Fuling shale gas field and predicting their spatial distribution. This successful study showcases the potential of this method for carrying out marine shale lithofacies prediction in China and other locations with similar geological backgrounds.

Main factors controlling the enrichment of shale gas in the Wufeng Formation–Longmaxi Formation in the Jiaoshiba area, Fuling shale gas field

Main factors controlling the enrichment of shale gas in the Wufeng Formation–Longmaxi Formation in the Jiaoshiba area, Fuling shale gas field

Methane content and isotopic composition of shallow groundwater: implications for environmental monitoring related to shale gas exploitation

The baseline methane for shallow groundwater can provide an important evidence to interpret possible methane stray associated with shale gas exploration. This study investigated and traced methane content and its origin of shallow groundwater in a karst aquifer in the Fuling shale gas block, SW China. The results show that methane contents of shallow groundwater are all less than 0.01 mg L−1 and volumetric content in dissolved gas ranges from not detected to 0.0064%. The δ13C-CH4 ranges from −74.4 to −49.1‰, suggesting biogenic origin. For the first time, the δ13C-CH4 and 3He/4He end-numbers were determined.

Application of Downhole Micro-seismic Technique in Shale Gas Fracturing Optimization of Fuling, China

The downhole micro-seismic method has successfully applied to well fractory fracturing development in Jiaoshiba block, Fuling shale gas reservoir in September 2015. The new concept and understanding have accumulated. Combing the actual construction condition of micro-seismic monitoring in JY AA-BB well groups, we reviewed briefly the downhole micro-seismic monitoring technology and then summarized multi-disciplinary experience and understanding. The staged fracturing process level improved and productivity increased with the further development of shale gas field. Results show that the understanding of micro-seismic method has played a guiding role in the optimization of fracturing process and site construction adjustment of other wells in the same area, which increased the productivity and created a huge economic benefits with a broad market prospects.

Geological controls and methane sorption capacity of marine shales of the Fuling shale gas field in the eastern Sichuan Basin, China

High-pressure methane sorption isotherms were performed on a series of Upper Ordovician Wufeng and Lower Silurian Longmaxi shale samples in the Fuling shale gas field to investigate the effects of organic matter content, thermal maturity, clay minerals, pore structure, temperature and pressure on methane sorption capacity. A large number of micropores with a pore width of less than 10 nm are developed within the organic matter, with its abundant specific surface areas as the fundamental factor to enhance the methane sorption capacity. The total organic carbon (TOC)-normalized sorption capacity increases with an increasing equivalent vitrinite reflectance R o , but an opposite trend is observed when R o is in the highly over-mature stage. The TOC-normalized sorption capacity shows no correlation with the total clay content as well as individual clay minerals. Most of the excess sorption capacity of shales increases with an increasing pressure, exhibits a maxima in the pressure range of 15–17 MPa and then decreases. The sorption isotherms show an obvious decrease in excess sorption capacity with increasing temperature. Moreover, the Langmuir pressure exponentially decreases with the reciprocal of temperature. Based on the Langmuir adsorption model, an empirical formula is established to evaluate the absolute sorption capacity of shales as a function of TOC content, pressure and temperature. Supplementary material: Additional description of experimental data are available at https://doi.org/10.6084/m9.figshare.c.3714040.v2

Application of surface–downhole combined microseismic monitoring technology in the Fuling shale gas field and its enlightenment

The Fuling shale gas field in the Sichuan Basin, as a national shale gas demonstration area, is the largest commercially developed shale gas field in the world except those in North America. The fracturing technology in the mode of “well factory” has been applied widely in the gas field, but it is necessary to perform further investigation on the way to evaluate effectively the fracturing effect of multi-well platform “well factory” and the distribution laws of its induced fracture networks. In this paper, the fractures induced by the “well factory” at the JY 48 platform were real-time monitored by a surface–downhole combined microseismic monitoring technology. The geometric size and extension direction of artificial fractures induced in the model of “well factory” fracturing in the Jiaoshiba block of Fuling Shale Gas Field were preliminarily understood. Moreover, the fracturing parameters under the mode of “well factory” were recognized by using the comprehensive interpretation results of surface–downhole combined microseismic monitoring technology, together with the SRV fracturing prediction chart. Eventually, the distribution laws of artificial fractures during the “well-factory-zipper” fracturing in the Fuling Shale Gas Field were clarified definitely. This paper provides guidance for the optimization of fracturing parameters at the later stage.

Cluster spacing optimization of multi-stage fracturing in horizontal shale gas wells based on stimulated reservoir volume evaluation

The multi-stage fracturing in horizontal well is a common technique for shale gas reservoir exploitation, in which cluster spacing governs the fracturing performance. Undersized cluster spacing might make the stimulated reservoir volume (SRV), activated by the respective hydraulic fracture, excessively overlap with each other, while oversized cluster spacing might leave a large unstimulated volume between neighboring hydraulic fractures; in either case, fracturing would be inefficient. Previous design of cluster spacing has failed to maximize the SRV due to the absence of a dynamic SRV evaluation model. A numerical model of SRV evaluation in shale reservoir was established by integrating four main modules, including fracture propagation, reservoir pressure distribution, formation stress distribution, and natural fracture failure criterion. Then, a method to optimize cluster spacing was developed with the goal of maximizing SRV. In order to validate this method, it was applied in Fuling shale gas reservoir in Southwest China to determine the optimal cluster spacing. The sensitivity of key parameters on the optimal cluster spacing has been analyzed. This research proposed a compelling cluster spacing optimization method, which could reduce the uncertainty in cluster spacing design, and provides some new insights on the optimal design of multi-stage fracturing in horizontal shale gas well.

Geochemical characteristics of gases from the largest tight sand gas field (Sulige) and shale gas field (Fuling) in China

This study performed a detailed geochemical analyses of the components, stable carbon isotopes of alkane gas and CO2, stable hydrogen isotopes of alkane gas and helium isotopes of reproducing gas from the largest tight gas field (Sulige) and shale gas (Fuling) field in China. The comparative study shows that tight gas from the Sulige gas field in the Ordos Basin is of coal-derived origin, which is characterized by a positive carbon and hydrogen isotopic distribution pattern (δ13C1 > δ13C2 > δ13C3 > δ13C4; δ2H1 > δ2H2 > δ2H3), i.e., the carbon and hydrogen isotopes increase with increasing carbon numbers. Carbon dioxide from this field are of biogenic origin and the helium is crust-derived. Shale gas from the Fuling shale gas field belongs to oil-derived gas which has complete carbon and hydrogen isotopic reversal of secondary alteration origin (δ13C1 < δ13C2 < δ13C3; δ2H1 < δ2H2 < δ2H3), i.e., the carbon and hydrogen isotopes decrease with increasing carbon numbers. Such complete isotopic reversal distribution pattern is due to the secondary alteration like oil or gas cracking, diffusion and so on under high temperature. In that case, positive carbon or hydrogen isotopic distribution pattern will change into complete isotopic reversal as the temperature increases. Carbon dioxide is of abiogenic origin resulting from the thermal metamorphism of carbonates and helium is crust-derived.

Geochemical features and genesis of shale gas in the Jiaoshiba Block of Fuling Shale Gas Field, Chongqing, China

Taking natural gas from marine strata of the Wufeng–Longmaxi Formation in the Jiaoshiba Block of the Fuling Shale Gas Field as a research subject, the analyses of the gradients of shale gas and carbon isotope shows that the natural gas from the Jiaoshiba area belongs to a high-quality hydrocarbon gas. The contents of methane range 97.22%–98.41%, with a little amount of ethane and propane, an average wetness of 0.74%, and little amount of non-hydrocarbons such as CO2, N2, H2, however, there's no H2S. The carbon isotopes of methane, ethane, and propane are characterized by their complete isotopic reversal (δ13C1 > δ13C2 > δ13C3). The natural gas from the Wufeng–Longmaxi Formation comes from the source rocks of the same formation, it classifies as a typical shale gas. According to the statistical determination criterion, natural gas in the Jiaoshiba area is derived from the sapropelic source rocks, which is a result of high-temperature pyrolysis. It is the product of mixing primary kerogen pyrolysis and secondary pyrolysis of crude oil, with apparent features of secondary pyrolysis of oil. The reason for the complete carbon isotopic reversal is the mixing of the two aforementioned gasses. Moreover, it has some sort of relationship with the loss function of shale gas after the Late Yanshan.

Features of the first great shale gas field in China

On the 28th of November 2012, high shale gas flow was confirmed to be 203 × 103 m3 in Longmaxi Formation; this led to the discovery of the Fuling Shale Gas Field. On the 10th of July in 2014, the verified geological reserves of the first shale gas field in China were submitted to the National Reserves Committee. Practices of exploration and development proved that the reservoirs in the Fuling Shale Gas Field had quality shales deposited in the deep-shelf; the deep-shelf had stable distribution, great thickness with no interlayers. The shale gas field was characterized by high well production, high-pressure reservoirs, good gas elements, and satisfactory effects on testing production; it's from the mid-deep depth of the quality natural gas reservoirs that bore high pressure. Comprehensive studies on the regional sedimentary background, lithology, micropore structures, geophysical properties, gas sources, features of gas reservoirs, logging responding features, and producing features of gas wells showed the following: (1) The Longmaxi Formation in the Fuling Shale Gas Field belongs to deep-shelf environment where wells developed due to organic-rich shales. (2) Thermal evolution of shales in Longmaxi Formation was moderate, nanometer-level pores developed as well. (3) The shale gas sources came from kerogens the Longmaxi Formation itself. (4) The shale gas reservoirs of the Fuling Longmaxi Formation were similar to the typical geological features and producing rules in North America. The findings proved that the shale gas produced in the Longmaxi Formation in Fuling was the conventional in-situ detained, self-generated, and self-stored shale gas.

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

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 × 104 m3, 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 × 108 m3. 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 × 104 m3/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.

The Fuling Shale Gas Field — A highly productive Silurian gas shale with high thermal maturity and complex evolution history, southeastern Sichuan Basin, China

The organic-rich Lower Silurian Longmaxi and Upper Ordovician Wufeng Shale (LSLUOWS) is one of the most important marine shale gas plays in southern China, with relatively high thermal maturity and complex structural evolution. The delineation of the Jiaoshiba shale gas play has been highly successful for the LSLUOWS in the Fuling area of southeastern Sichuan Basin. The drilling targets the basal part of the LSLUOWS, where the approximately 38–45 m of organic-rich (total organic carbon of greater than 2%) section corresponds to a maturity range around 2.2%–3.0% Ro, with high brittle mineral content (55%–65%). The produced shale gas displays a clear reversal in the stable carbon isotopes. The shale gas play zone is between the overlain mudstone in the Middle-Upper Longmaxi Formation (Fm) and the underlain Upper Ordovician tight limestone in the Jiancaogou Fm. The shale gas reservoir is overpressured, with an average pressure coefficient of 1.55 (relative to hydrostatic pressure). From December 2013 to late 2014, results of production tests determined relatively stable pressure and production curves. Fifty prolific gas wells have been completed to date in the Jiaoshiba Shale Gas Field in Fuling. Preliminary study revealed several characteristics of this structurally complex shale play that are distinctly different from those in the United States, including an anticlinal structure with mild deformation, abundant free gas, and very short gas migration through microfractures, the natural fracture network formed by the two fault systems, and the slip parallel to the layer in the basal LSLUOWS. Movement along strike-slip faults has gone through up into the Quaternary, which is considered to be a significant factor in the establishment and preservation of the overpressured region in the LSLUOWS.