Control Sulfur Control Iron Containing Hydrogen Sulfide Gas Well Acidizing And Acid Fracturing Technology Research

Sour gas reservoir that contains hydrogen sulfide has special properties with high embedding depth, high formation temperature and low permeability, which occupies approximately twenty-five percent of the whole gas resources in our country. Safe and effective exploitation and utilization of the sour gas reservoir play greatly important roles in realization of natural gas industry harmony and alleviation unbalance of supply and demand for natural gas. Sour gas reservoir with strong character brings about much difficulty in its reforming. Experience in existence on sour gas reservoir reforming at home and abroad shows that hydraulic fracture technique often confront with technical problems such as high injection pressure, high fluids loss velocity, serious water block, low fracture conductivity, hard cross-linking and decomposing of gel. So, hydraulic fracture technique often meets failure in reforming the formation of a sure gas reservoir which contains H2S. On the contrary, acid fracturing technique is more effective to recover a sour gas reservoir with hydrogen sulfide than hydraulic fracture technique. Acid fluids adapt to sour gas reservoir formation reforming experienced a long period of time about 30 years at abroad, and two type of representative acid fluids , gel acid and emulsified acid, come into being gradually. Unfortunately, some technical problems urgent to be solved still exist, such as rapid acid reaction to carbonate rock, very short effective distance of acid penetration, serious iron sulfide precipitation, sulfur precipitation and H2S corrosive action.Based on chemical thermodynamics theory and ion equilibrium theory, this thesis systematically analysis and contrast the precipitate behavior between ferric, ferrous and sulfide under different conditions with H2S present and H2S not present, and then put forward a set of iron control and sulfur control method for the first time. The secret of iron control and sulfur control method is that a sulfur modifier developed in the thesis can react directly with hydrogen sulfide and form highly soluble complex avoiding large dosage of mutual solvents to control sulfur precipitate in general method at abroad. This method shows substantial differences with that of routine method. The chelating agents and sulfur modifier used at one time can effectively control iron precipitate and sulfur precipitate problems, which may contribute to recovering of sour gas reservoir. Aimed at the character of sour gas reservoir, the thesis developed a contraposed acid fluid, emulsified acid, that bears high viscosity and low flowing resistance and put forward a newly effective emulsifier. The fitness of emulsified acid is improved by lots of tests and rtheology experiments. Rock samples came from Changxing formation layer, Jian Nan gas field, were prepared for loop experiment. The reaction mechanism between emulsified acid and carbonate rock samples and conductivity of etching map that the acid-rock reaction had left was studied systematically according to many set ofloop experiments fulfilled in loop Lab. At the same time, the feasibility of emulsified acid schlepping solid technique was proved in loop experiment. On the basis of the tests results of parallel plates reaction model, the thesis established the acid concentration distribution model in fracture length, the fracture width enlargement at different location and time and the acid front velocity model. The acid fracturing technique fit for Changxing formation, Jian Nan gas field, was chosen out based on the loop experiments.