Sandstone Reservoirs Acid Fracturing Feasibility Study

Acid fracturing is generally applied in carbonate reservoir. It is believed that sandstone reservoir generally uses hydraulic fracturing, and acid-washing or matrix acidizing when removing the plug near wellbore. But whither sandstone reservoir can be stimulated with acid fracturing or not causes people's great concern in recent years. Some oilfield has succeeded when trying by acid fracturing in sandstone reservoir. The paper analyses the reasons that sandstone reservoir can't apply acid fracturing to stimulate generally, and the corresponding possible condition have been put forward in accordance with its reasons. The possible condition is analyzed and validated from theory, lab and on-spot successful apply. The achievements made is as follows:1 .Theory analyse indicates that sandstone acid-rock reaction is complicated, The chemical reaction of HF and aluminium silicate is divided into three steps, and HF molecule is the main function type, HC1 has accelerated HF speed of the dissolve to the mineral. The production of acid-rock reaction has much secondary precipitation, but which can use chemistry, suitable acidizing fluid type and concentration, correct acidizing treatment technology to control the quantity, so reduce the damage of precipitation to formation. Acid-rock of sandstone Reaction rate is controlled by surface reaction generally, and rotatory disc is used commonly to mensurate reaction kinetics, but the HF concentration is more difficult to determine because of its ionization.2.The suitable acidizing fluid type and concentration used in acid fracturing for sandstone formation must meet the needs of reducing the secondary precipitation and preventing plugging the stream of acid etching from it, and the needs of having enough strength of dissolving to rock to form acid etching, reducing the damage to rock matrix and stabilize particle. The experiment result of acidizing fluid formula with the cores of JiangSu oilfield indicates that the acidizing fluid can meet the request of acid fracturing in sandstone by optimizing acidizing fluid type and its concentration, and that the testing way of utilizing silver paper to support twosymmetrical core to simulate certainly sew width is inadvisable lab method to run flow experiment, and circulation device is the suitable equipment.3.The more important thing which sandstone reservoir can be stimulated with acid fracturing is that the acid etching fracture has fine fracture conductivity after acidizing treatment. The suitable acidizing fluid formula and acid fracturing technology can be optimized by mensurating the fracture conductivity and its influence factor. The experiment result of fracture conductivity of acid etching proves that optimizing acidizing fluid formula can prevent sandstone rock from structure destroy and sand production, and can obtain high fracture conductivity.The numerical simulation methods of fracture conductivity are provided too in the article at the same time , including the N-K experience relational expression commonly used and the new model which considers the roughness of acid etching and the acidizing treatment process.4.Acid concentration distribute form of acid fracturing in sandstone is as same as that in carbonate, just boundary condition is different, and surface concentration and diffusion coefficient in the equation are comparatively difficult to confirmed.5.Considering the character, mineralogical and cementation type of sandstone formation, the sandstone formation can apply acid fracturing by optimizing acidizing fluid type and its concentration if the buried depth of formation is not deep, the HC1 dissolvability is high and cementation is fine. The water injection well of sandstone reservoir may succeed more than production well if taking acid fracturing treatment because reducing of effect closed pressure on acid etching fracture. Combining the acid fracturing technique in carbonate formation and the acid fluid characteristic in sandstone formation acidizing treatment, the acid fracturing technique in sandstone formation is dis...