Research On Technics Of Low Damage Acid Fracturing And Elemental Sulfur Deposited In Sour Gas Reservoir

Sour gas, one of the most important parts of unroutine nature gas, is very rich in SiChuan basin and BoHaiwan basin of China and its proved geologic reserves had excessed 5000 × l0~8m~3.Safe and effective exploitation of sour gas reservoir plays greatly important roles in dealing with increasingly serious conflict between the development of social economy and energy. It, however, confronts some difficult problems,such as corrosivity of hydrogen sulfur, elemental sulfur deposition and low damage acid fracturing. Solving all of these problems is foundation and hypothesis to exploitate sour gas reservoirs.This thesis developed two aspects of effectively exploitate sour gas reservoirs, including technology of low damage acid fracturing and sulfur deposition in formation and fracture while gas well produce. The first one mainly studied on the method preventing iron and element sulfur precipitating in process of acid fracturing, decreasing formation damage. Based on fundamental theories, the last one modeled the performance of sulfur deposited in formation and fracture when gas well produced. It is not only practical to analyze the influencing factors of sulfur deposition, dynamic parameters of well and fracture, also can make reference to optimize fracturing design.Based on chemical thermodynamics theory and ion equilibrium theory, it analyzed and contrasted the precipitate behavior between ferric, ferrous and sulfide under different conditions. It gets an emulsified acid system which was composited with rephyticacid, sulfur modifier and H2S scavengers. Experiments shows that this emulsified acid system can strongly control reaction between iron ion and sulphur ion and preventing iron ion and sulfur precipitating. At the other hand, H2S Scavengers can shield or consume hydrogen sulfur which may react with iron ion, decreasing probability of precipitate of iron ferrous and elemental sulfur and enhancing stimulation effect.It's familiar that elemental sulfur deposited in reservoir and product line, which not only brings great endanger to equipment, but also makes formation or fracture be plugged. It's one of important keys that influence effective and economic exploitation of sour gas reservoir. In this section, it started with discussing mechanism of sulfur deposited in reservoir and interrelated keys that impacts on it. And then developed mechanism of percolation channels being plugged by sulfur particles on the view of microcosmic and analyzed the impaction of gas hydrodynamic on transporting and movement of sulfur particles, building corresponding critical mathematical models.