New shale gas well fracturing technology and its application

shale gas because of its low permeability reservoirs, gas occurrence diverse characteristics, determined using conventional fracturing the formation of a single fracture stimulations shale gas technology has been unable to meet the transformation, we must explore and study new fracturing modification techniques in order to enable them to make effective economic development.

First, the basic characteristics of shale gas

Shale gas mining depth generally less than 3000m, its typical characteristics of the reservoir as follows: ① quartz content greater than 28%, typically 40% to 50%, the damage will produce complex seam network; ② dense shale gas reservoirs, pore degree was 4.22% ~ 6.51%, matrix permeability in 1.0mD the following; ③ micro-fractured shale, shale gas development in the fracture network system is not the case, it is difficult to become effective reservoir; ④ shale gas abundance of organic matter , thickness, organic carbon content is generally greater than 2%, maturity of 1.4% to 3.0%, to I ~ Ⅱ kerogen type-based, effective thickness is generally 15 ~ 91m; ⑤ shale brittleness coefficient, easy to form shear cracks, such as Young's modulus of the Barnett Shale 34000 ~ 44000mPa, Poisson's ratio of 0.2 ~ 0.3; ⑥ shale gas are adsorbed and dissolved state and the free state three kinds of occurrence, its occurrence requires a large transformation of volume, this will obtain high yield.

Second, the volume of shale gas well fracturing technology

Volume fracturing refers to  Hydraulic fracturing  process, so that the continuous expansion of natural fractures and brittle rock slip shearing, forming a natural and artificial crack crack crack intertwined network, thereby increasing the reconstruction volume, improve initial production and ultimate recovery rate.

Shale gas reservoir permeability low, thick, natural fractures, mainly in the adsorbed gas adsorbed on the surface of organic matter, the conventional transformation form a single crack is difficult to obtain a good yield. Numerical simulation shows that the volume of shale gas reservoir reconstruction greater yield after pressure better. But to achieve volume reconstruction, in addition to the volume fracturing the formation to have the basic conditions, the fracturing process method is also very crucial.

1 large vertical wells slick water fracturing technology

(1) Fracturing Process

Fracturing the concept of "two, two small" feature, "two" means: ① large displacement, displacement 10m3/min construction above; ② large amount of fluid with a single well fluid volume 2271 ~ 5678m3. "Two small" means: ① a small particle diameter proppant  Proppant  generally of 70/100 mesh and 40/70 mesh ceramic; ② lower than sand, sand-liquid ratio of the average 3% to 5%, the highest sand liquid ratio not more than 10.0%.

(2) fracturing fluid system

Fracturing fluid system in slippery water-based, slippery water anionic polymers can be used, you can also use low concentrations of guar gum.

2 horizontal well fracturing technology clustering segmentation perforating

(A) clustering perforating technology

In order to form a mesh fracturing cracks, improve reconstruction volume, the use of clustering perforating technology, every 4 to 6 fractions perforation clusters, each cluster length 0.46 ~ 0.77m, cluster spacing 20 ~ 30m, phase angle of 60 ° or 180 ° , the hole density 16 ~ 20 holes / m, diameter 13mm.

(2) Construction steps staged fracturing technology

Construction steps as follows: ① the first paragraph using tubing or coiled tubing conveyed perforating, perforating gun made; ② conducted from the first paragraph of the annulus fracturing; ③ gel wash wellbore; ④ liquid pumped cable + guns + bridge plug tools into the well; ⑤ electrically detonated seat seal bridge plugs, perforating gun and the bridge plug separation, pressure test (approximately over perforations 25m); ⑥ drag cable with perforating gun to perforation, perforation, drag cable; ⑦ fracturing the second layer, repeat steps ④ ~ ⑦, to achieve multi-staged fracturing.

(3) bridge plug after pressure treatment

After pressure with coiled tubing milling or φ73mm + φ101.6mm diamond blade knife out of 5 bridge plug, drain seeking bonding layer production.

3 shale gas volume effect of reconstruction

Using the above method, micro seismic waves through the underground tests confirmed slippery shale gas water mass fracturing vertical wells and horizontal wells perforating clustering segmentation cracks fracturing the formation of networks and improve the fracture volume.