Daniudi gas field consists of He 2 and He 3 gas reservoirs, which are located in the north of Yishan slope and controlled by regional structure. The structure of He 2 and He 3 gas reservoirs is gentle, and the overall performance is characterized by west dip monoclinal structure. Daniudi gas field is generally a gentle monocline with a dip angle of 0.3 ~ 0.6, and a nose uplift is developed locally. Judging from the test results and gas layer distribution, the structure has no obvious control effect on oil and gas distribution.
Sedimentary characteristics
The second and third stages of Xiashihezi Formation belong to fluvial sedimentary environment, and channel sand bodies form reservoirs. The thickness of single-layer sand body is generally around 10m, and the lateral change of sand body is rapid. During the sedimentary period of Xiashihezi Formation, due to the rapid uplift of provenance in the northern part of the basin, the supply of terrigenous clastic materials was sufficient, the surface alluvial water system was developed, and river deposition was widespread. In the vertical sedimentary sequence, coarse-grained sediments are dominant, showing positive cycle characteristics, with gravel in the lower part, coarse sandstone and medium sandstone in the upper part, and abrupt contact with mudstone at the top. The meandering river "binary structure" can be seen in some wells of He 3 member, but the He 1 member and He 2 member are not obvious. The sand-mud ratio and sand-soil ratio in the section from Box/Kloc-0 to Box 3 gradually decrease, indicating that the deposition of Xiashihezi Formation has a tendency of gradual transition from braided river deposition to meandering river deposition, but braided river is still the main one on the whole (Figure 5-1 2).
The sedimentary microfacies of reservoir are beach and river filling microfacies, and the lithology is mainly gray and light gray gravelly coarse sandstone, coarse sandstone and a small amount of glutenite and fine conglomerate. Sandstone is very thick.
Figure 5- 12 Comprehensive Sedimentary Profile of Upper Paleozoic in Daniudi Area
Reservoir characteristics
Reservoir lithology is mainly composed of coarse detritus in timely sandstone, coarse detritus in timely sandstone and clastic sandstone. Pore types are mainly intergranular, intragranular dissolved pores and residual intergranular pores formed by dissolution, and pore throats are characterized by small pores and thin throats, belonging to reservoirs with low porosity and low-ultra-low permeability (Tables 5-2 and 5-3).
Table 5-2 Statistical Table of Reservoir Physical Properties of He 2 and He 3 Gas Reservoirs in Daniudi Gas Field
5.4.4 Source-reservoir-cap assemblage
During the transitional period between land and sea, the upper Paleozoic sediments developed from Taiyuan Formation and Shanxi Formation to Box 1 delta plain, forming a self-generating and self-storing combination with large contact area. By the 2nd and 3rd member of Box 2, it has been transformed into braided river-meandering river sedimentary system, forming a source-reservoir-cap assemblage of lower generation, middle storage and upper cover. The argillaceous rocks of the Upper Shihezi Formation are the regional caprocks of various gas reservoirs in the Upper Paleozoic (Figure 5- 13).
Table 5-3 Statistical Table of Mercury Parameters in Box2 and Box3 Gas Reservoirs of Daniudi Gas Field
Figure 5- 13 Gas Reservoir Profile of Well Da 4-Well Da 7 in Daniudi Gas Field
Trap type
The target traps in Daniudi gas field are lithologic traps, which can be divided into sandstone pinchout traps and diagenetic traps. Lithologic traps are mostly "three-layer structure" mode of reservoir+tight transition zone+caprock (Figure 5- 14 and Figure 5- 15), which are common both vertically and horizontally. This reservoir-cap combination model always leads to the thickness of effective gas layer being smaller than that of sand interval, and there is a big gap between the effective gas-bearing range on the plane and the adjacent range of sandstone, thus predicting the gas reservoir and gas layer scale.
5.4.6 Migration characteristics and accumulation of natural gas
The He 2 and He 3 gas reservoirs in Tabamiao area belong to the reservoir-forming combination of lower and upper reservoirs and caprocks, and are secondary migration and accumulation. Vertical gaseous hydrocarbons need to be transported from source rocks of Taiyuan Formation and Shanxi Formation to Xiashihezi Formation, and the distance is about100 ~ 250 m ~ 250 m. ..
5.4.7 Fluid characteristics and gas reservoir types of gas reservoirs
The measured formation pressure of Daniuhe 2+3 gas reservoir is 2 1.94 ~ 26.43 MPa, the pressure coefficient is 0.9 1 ~ 1.02, and the gas reservoir pressure gradient is1.16mpa/100m. The results of gas test and fluid sample analysis show that the gas reservoir of box 2+3 in Daniudi gas field mainly produces natural gas, and the methane content in natural gas accounts for 96% ~ 98% of total hydrocarbons, and the content accounts for 2% ~ 4% of total hydrocarbons, which belongs to dry gas. Very little oil is produced, with a density of 0.7 ~ 0.8g/cm3, kinematic viscosity 1.06 ~ 1.6μ m2/s, initial boiling point temperature 10 ~ 135℃, and 95% distillation range temperature generally less than 300℃, which is low density. There is no water output. To sum up, the gas reservoir in He 2+3 member of Daniudi gas field is a lithologic gas reservoir with low-ultra-low permeability and infinite bottom water constant volume elastic drive.
Figure 5- 14 Dakai 15 Well 2 Reservoir-Cap Combination Form
5.4.8 Controlling factors of reservoir formation
1) The mudstone of Shiqianfeng Formation and Shangshihe Formation are good regional caprocks, with thick mudstone and common overpressure. The thick mudstone of Shangshihe Formation has the highest overpressure, which is formed in Cretaceous gas reservoirs, and the mudstone of Shangshihe Formation is a high-pressure sealing layer (Figure 5- 15).
Figure 5- 15 Reservoir Profile of Daniudi Gas Field
2) The west and south sides of Daniudi Gas Field are adjacent to the gas production center (Figure 5- 16), and the gas originated from the Middle and Late Triassic and experienced five stages of filling from the Middle Cretaceous, with sufficient gas sources; The formation and distribution of gas reservoirs are mainly controlled by the distribution of NE-trending superimposed sandstone bodies, and have nothing to do with structural position.
Fig. 5- 16 hydrocarbon generation intensity map of upper Paleozoic source rocks in Ordos basin
3) The north is close to the provenance, and the alluvial fan and channel sand bodies are coarse in lithology, with great changes in physical properties and dense reservoirs. Therefore, the close contact between low permeability reservoirs and gas source rocks is mainly controlled by easy formation of physical properties and lithologic pinch-out, and regional hydrodynamic sealing is also an important reservoir-forming factor.
The petroleum system of Upper Paleozoic in Daniudi area in the north is divided into three sets of gas-bearing reservoir-forming combinations. In addition to the gas-bearing reservoir-forming assemblages of Box 2 and Box 3, there are two gas-bearing reservoir-forming assemblages of Shan 1-2 and Tai 2 * *, among which Shan 1-2 is the main one.