1. Development Difficulty of Thin Layer Low-seepage Thickened Oil
The characteristics of Thin Layer Low-seepage Thickened Oil:
ⅰ.Lots of thin layers and interlayers：Oil reservoir thickness <10m, development of inter-bed and strong interlayer non-homogeneity leading to unbalanced thermal recovery, great steam injection thermal losses and poor thermal recovery effect.
ⅱ.Low permeability: Low permeability, high steam injection pressure, large recovery oil resistance, and progressive decrease
ⅲ.High clay content: Average >10%, easy blocking of immediate vicinity of wellbore and sand filter pipe by argillaceous cement, and quick declining of wellhead yield.
Above factors cause Single-well low production and low efficiency.
2. Introduction to Fracturing Sand Prevention Process
Fracturing sand prevention process is a kind of production increase sand prevention technology effectively integrating the sand prevention process with the fracturing process. After the fracturing sand prevention tubular column is tripping in, the formation shall be pressed into a short and wide crack. The crack shall be filled with considerable gravel. Then, the pipe shall be subject to circulating filling with annular gravel.
Strong theoretical pertinence, Strong field adaption:
2.1 Lots of thin layers and interlayers
The vertical fissure formed by fracturing sand prevention can communicate various small layers, take full advantage of the overlapping function of steam, and improve the thermal recovery effect.
2.2 Low permeability
Short and wide gap formed by fracturing sand prevention can improve the permeability of immediate vicinity of wellbore and the reservoir steam absorption capacity, and reduce the steam injection pressure.
2.3 High clay content
The bilinear flow pattern remits the carrying of mud. Artificial sand plays a role in resisting migration of formation silty-fine sand and mud. 3. Advantages of Fracturing Sand Prevention Process
3.1 Large sand prevention reconstruction radius
3.2 Strong comprehensive production increase effect
Dual-function of production increase and sand prevention：Fissure with high flow conductivity makes Production increase.Rock matrix reinforced by sand bridge plug made sand fixed. 4. Construction of Fracturing Sand Prevention Process
4.1 The key operation point：
ⅰ.Low preposition Increase fissure width
ⅱ.High sand ratio Improve fissure flow conductivity
ⅲ.Weak crosslinking Promote end sand removal to form short and wide gap
Ultimately, Short and wide gap with high flow conductivity should be constructed.
4.2 Integral work string:
At one stroke, fracturing sand prevention integral tubular column can finish formation fracturing filling and annular filling, which is favorable for end sand removal to form protection of short and wide gaps. The tubular column can properly protect the casing above the packer.
5.Application Effect of Fracturing Sand Prevention Process
5.1 Upgrading of reserve utilization of low-quality thickened oil
Case: T38 Region belongs to a typical low-quality thickened oil reservoir of Sinopec SHENGLI Oil Field. Due to thin reservoir, high ash content, strong water sensitivity, thickened oil and other factors of Sand Groups II and IV, the development technology is inapplicable. Moreover, 6.9 million tons of reserves cannot be effectively utilized.
ⅰ.Lots of layers, thin layer and low net total ratio: The average thickness of oil reservoir is approximately 1.6m. The 5-layer superposition thickness is 9.8m. The net total ratio is 0.26.
ⅱ.High clay content and strong water sensitivity: The shale content is 9-16.9%. According to the thin section analysis, the clay minerals mainly include montmorillonite. As it swells in the water, it will block the throat, with strong water sensitivity. The water sensitivity index is above 0.995.
ⅲ.Sand & mud of formation and serious blocking: Shallow burial depth (750m-1,000m), weak compaction, poor lithology, mainly of argillaceous and heavy crude oil cementation, and easy sand and mud blocking caused by clay swelling and migration.
ⅲ.High crude oil viscosity, and insufficient natural energy: High crude oil viscosity (10,000-16,000mPa.s) and poor natural energy leading to extremely insufficient liquid supply capacity of oil well.
The first appraisal well in this block was finished in Fe.2010. In Mar. 2010, S43 was subject to formation testing, with the thickness of 12m/2 layers. Swabbing proved thickened oil with large viscosity and poor physical-property contrast. It is incapable of exploitation and well sealing. In Dec. 2011, this well was subject to fracturing filling for sand prevention outside the pipe steam injection thermal recovery (sand added: 48m3) steam injection thermal recovery, obtaining stable productivity. Thus, a breakthrough was made in the production process.
The fracturing sand prevention process was adopted for this block in 2012-2015. The matching horizontal shaft realized effective reserve utilization of low-quality thickened oil. Utilized reserves: 2,150,000T Total number of wells: 28 (16 new wells 2 old wells) Average single control: 78,000T.
5.2 Substantial improvement to yield of old wells after reconstruction
Effect comparison of Gao XX Block after Single-well Sand Prevention
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