【ECF News】China's definition for shale gas, tight oil and shale oil
I. Shale Gas
Standard: National Standard GB/T31483-2015 "Shale gas geological evaluation method", issued by the General Administration for Market Regulation and the Standardization Committee of China in May 2015.
Definition: The shale gas is mainly composed of free or adsorption state natural gas in the organic-rich shale interval. The main body is self-generated and self-storing, large-area continuous natural gas accumulation. Under overburden conditions, the shale matrix permeability is generally less than or equal to 0.001 mD. Single well generally has no natural production capacity, requiring certain technical measures to obtain industrial gas flow.
There are 3 major concepts in the definition:
1. Shale: A grainy and brittle fine-grained sedimentary rock that consists of granular debris, clay, organic matter, etc. with a particle size of less than 0.0625 mm.
2. Organic-rich shale: Dark-colored shale with more than 2% organic carbon content in rocks and more than 1% in other types.
3. Organic-rich shale interval: Geology units of thin interlayers between organic-rich shale and stratigraphic units rich in organic shale and silty sandstone, fine sandstone or carbonate rock. Wherein, the thickness of the single layer of the thin interlayer is not more than 1 m, and the thickness of the accumulated thin interlayer accounts for less than 20% of the total thickness of the shale layer.
Minimum industrial gas flow standard for shale gas wells
| Depth (m) | Vertical Well Production (10,000 m3/d) | Horizontal Well Production (10,000 m3/d) | Conventional Onshore Vertical Well Gas Production (10,000 m3/d) |
| <500 | - | - | 0.05 |
| 500-1000 | 0.20 | 1.00 | 0.10 |
| 1000-2000 | 0.50 | 2.00 | 0.30 |
| 2000-3000 | 1.00 | 4.00 | 0.50 |
| 3000-4000 | 2.00 | 6.00 | 1.00 |
| 4000-4500 | 3.00 | 8.00 | 2.00 |
II Tight Oil
Standard: National Standard GB/T34906-2017 "Geological Evaluation Method for Tight Oil", issued by the General Administration of General Administration for Market Regulation and the Standardization Committee of China in November 2017.
Definition: The oil in the reservoirs of tight sandstones, tight carbonates, etc. with a permeability of less than or equal to 0.1 mD (air permeability less than 1 mD), or non-heavy oils with a fluidity of less than or equal to 0.1. mD/(mPa.s).
The reservoir is adjacent to organic-rich oil rock. The single well has no natural production capacity or natural production capacity lower than the minimum commercial oil production, but commercial oil production can be obtained under certain economic conditions and technical measures.
What makes sense is that in this standard, the indicators and thresholds for the geological evaluation of the tight oil sweet-spots area are determined. In addition to geological sweet-spots and engineering sweet-spots, the evaluation of economic sweet-spots is also emphasized.
Another important indicator is that the standard sets weights for each evaluation index. Of course, these weights are only a reference standard. Due to the differences in geological foundations and reservoir conditions of various basins and reservoirs. The geological indicators and weights should vary in the standard.
