ZM gas reservoir located in Shanxi province of China is a significant development and evaluation block of PetroChina. It belongs to low porosity and low permeability reservoir. Although most of the wells adopt the technology of layered fracturing and commingled production because of low psotfrac output of individual layer, the production is generally low. This paper systematically evaluates the fracturing data, analyzes fracturing operation curves, optimize the fracture parameters and study the technology for improving fracturing effects.
In 2006, 63 wells (101 layers) in ZM gas reservoir adopted hydraulic fracturing including individual layer fracturing in 32 wells and layered fracturing in 31 wells. First, utilize the fracturing data in 2006 to comprehensively analyze the relations between formation parameters and different fracturing data including fracturing scale, fracturing effects and fracturing operation parameters, and simulate the fracture geometry in use of FracproPT software. Moreover, all the fracturing operation curves are analyzed and some useful information was acquired which indicates the formation character and also some operation problems, especially the rapid propagation of fracture height. Considering the thickness and permeability of fracturing formation and the differences of interlayer thickness in ZM gas reservoir, we optimize the fracture parameters and recommend the fracturing operation scale. Finally, the fracturing technology is studied for improving fracturing effects in ZM gas reservoir.
ZM gas reservoir is located in Shanxi province of China, and its buried depth is 2200–2800m. Its producing formations include the second section of Shanxi group, eighth section of Shihezi group and Taiyuan group. The main lithology is silicarenite. In second section of Shanxi group, the average porosity is 4.1%, and the average permeability is 0.33?10−3 µm2. In eighth section of Shihezi group, its average porosity is 5.3%, and average permeability is 0.51?10−3 µm2. The average porosity of Taiyuan group is 6.2%, and permeability is 0.89?10− 3 µm2. The gas pressure of Shanxi group is 22.92–25.43MPa, and pressure coefficient is 0.9–1.02. For Shihezi group, the pressure coefficient is 0.85–0.9, and temperature gradient is 2.99_/100m. Most of the wells adopt the technology of layered fracturing and commingled production because of low psotfrac output of individual layer.
Relationship between fracturing scale and formation parameters
Fig 1 and fig 2 are the relation curves of proppant concentration and formation parameters through statistic data. Most of the proppant concentration is between 2–8m3/m. With the increase of permeability and formation capacity, the proppant concentration decrease a little. When formation capacity is more than 10mDc.m, the proppant concentration is only about 3m3/m which is lower.
Fig 3 and fig 4 are the relation curves of proppant concentration and formation thickness through statistic data. With the increase of effective thickness, the proppant concentration decreases a little. When formation thickness is 15m around, the concentration is only 3–4m3/m which is lower than 5–10m3/m of thin layers less than 5m. High proppant concentration for thin layers increases the treatment risk to some extent. At the same time, low concentration for thick formations will decrease stimulation effects.
