Lacustrine Shale Gas Occurrence Characteristics

The seventh member of the Yanchang Formation, Upper Triassic black shale deposited in the deep and semideep lacustrine environment, is located in the southeast area of the Ordos Basin. It is 1200–1800 m in buried depth and 30–60 m in thickness. As the main target of lacustrine shale gas in this region, the seventh member of the Yanchang Formation usually uses fracturing technology as the major stimulation treatment. Slick-water fracturing with a high-pumping rate has been successful early on, but the low reservoir pressure of this formation resulted in a large volume of fracturing fluid invasion. As a consequence, the shale-gas well production has been postponed owing to the low rate of fracturing-fluid flowback and a long cleanup period. Liquid-[Formula: see text] fracturing has caused almost no damage to the formation, and the volumetric expansion of [Formula: see text] after gasification will increase formation energy and improve the fluid cleanup rate. I have developed a liquid-CO2/slick-water hybrid fracturing technology that combined the advantages of liquid-[Formula: see text] and high-pumping-rate slick-water fracturing. Sixteen vertical wells and one horizontal well have been tested in the Ganquan Area, Shaanxi Province, China. As a result, the fluid cleanup rate improved 30% in comparison with regular slick-water fracturing. Moreover, the fracturing-fluid cleanup period of vertical wells decreased from 45 to 25 days. A field test indicated that because more liquid [Formula: see text] was used (i.e., the volume ratio of liquid [Formula: see text] to slick water increases), the performance of reservoir energizing and flowback result improved.

Download Full-text

Evaluation Lacustrine Shale Gas Resources

Lacustrine Shale Gas ◽

10.1016/b978-0-12-813300-2.00006-4 ◽

2017 ◽

pp. 289-329

Author(s):

Xiangzeng Wang

Keyword(s):

Shale Gas ◽

Lacustrine Shale

Download Full-text

Nanopore Structure and Fractal Characteristics of Lacustrine Shale: Implications for Shale Gas Storage and Production Potential

Nanomaterials ◽

10.3390/nano9030390 ◽

2019 ◽

Vol 9 (3) ◽

pp. 390 ◽

Cited By ~ 6

Author(s):

Lei Chen ◽

Zhenxue Jiang ◽

Shu Jiang ◽

Keyu Liu ◽

Wei Yang ◽

...

Keyword(s):

Fractal Dimension ◽

Surface Area ◽

Clay Minerals ◽

Shale Gas ◽

Negative Relationship ◽

Quartz Content ◽

Average Pore ◽

Positive Correlation ◽

Fractal Characteristics ◽

Lacustrine Shale

In order to better understand nanopore structure and fractal characteristics of lacustrine shale, nine shale samples from the Da’anzhai Member of Lower Jurassic Ziliujing Formation in the Sichuan Basin, southwestern (SW) China were investigated by total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM), and low-pressure N2 adsorption. Two fractal dimensions D1 and D2 (at the relative pressure of 0–0.5 and 0.5–1, respectively) were calculated from N2 adsorption isotherms using the Frenkel–Halsey–Hill (FHH) equation. The pore structure of the Lower Jurassic lacustrine shale was characterized, and the fractal characteristics and their controlling factors were investigated. Then the effect of fractal dimensions on shale gas storage and production potential was discussed. The results indicate that: (1) Pore types in shale are mainly organic-matter (OM) and interparticle (interP) pores, along with a small amount of intraparticle (intraP) pores, and that not all grains of OM have the same porosity. The Brunauer–Emmett–Teller (BET) surface areas of shale samples range from 4.10 to 8.38 m2/g, the density-functional-theory (DFT) pore volumes range from 0.0076 to 0.0128 cm3/g, and average pore diameters range from 5.56 to 10.48 nm. (2) The BET surface area shows a positive correlation with clay minerals content and quartz content, but no obvious relationship with TOC content. The DFT pore volume shows a positive correlation with TOC content and clay minerals content, but a negative relationship with quartz content. In addition, the average pore diameter shows a positive correlation with TOC content and a negative relationship with quartz content, but no obvious relationship with clay minerals content. (3) Fractal dimension D1 is mainly closely associated with the specific surface area of shale, suggesting that D1 may represent the pore surface fractal dimension. Whereas fractal dimension D2 is sensitive to multiple parameters including the specific surface area, pore volume, and average pore diameter, suggesting that D2 may represent the pore structure fractal dimension. (4) Shale with a large fractal dimension D1 and a moderate fractal dimension D2 has a strong capacity to store both adsorbed gas and free gas, and it also facilitates the exploitation and production of shale gas.

Download Full-text