Study On Low-damage Seawater-based Fracturing Fluid System In Bohai SZ36-1 Oilfield

In recent years, the strategic direction of oil and gas resources development is to move towards ocean, offshore oil and gas resources are very rich, but the unexpoited resource of low-permeable is low in the sea, which suggestes the good prospects of hydraulic fracturing techniques?With the limitation of platform conditions, ashore traditional batch mixing methed for preparing fracturing fluids is unfit for offshore, in order to reduce the limit of preparing liquid water requirements, to expand fracture scale, the on-the-fly mixing method directly with seawater will be widely applied in the future,which can inprove operational efficiency,save cost and increase fracture scale.However the problem of ordinary fracturing system can not solve to the problems dissolve slowly, low viscosity, crisp, poor temperature resistance in the high mineralized waters and the on-the-fly can not meet the requirements of offshore platform fracturing operation,Hence it is important to research the system of seawater-based fracturing fluids.In this paper, the synthesis of BCG-1S of seawater-based thickener was studied. According to the principle of molecular design, A gelatinizer(BCG-1S) was prepared by ternary copolymerization of acrylamide(AM), N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropy)ammonium(DMAPS) and hydrophobic monomer of Sixteen alkyl two methyl ammonium chloride (DM16), hydrolysis. The effects of initiator dosage, reaction temperature and other conditions on the solubility and apparent viscosity of copolymers were studied by single factor method. For synthetic polymer by IR and 1H-NMR the structure characterization, which confirmed the structure of the product is consistent with the original design. Viscosity average molecular weight is 5.97 million by the methold of intrinsic viscosity.Preparing fluids by the simulated seawater and evaluated BCG-1S the related performance.The results showed that the gelatinizer had a good rheology temperature and shearing resistance. The basic formula of seawater based fracturing fluids was determined by the screening of the increasing viscosity auxiliary agent, temperature stabilizer, gel breaking agent, anti-swelling agent and auxiliary agent.By the reparing fracturing fluids with the SZ36-1 seawater, reference to the petroleum and natural gas industry related evaluation standards,the comprehensive performance of the fracturing fluid was evaluated. the results showed that the fracturing fluids is a viscoelastic fluid with good carrying performance and abrasive resistance. The viscosity of the system of fracturing fluid remained at 40 mPa-s after sheared at shear rate of 170s"1 and temperature of 140? for 120 minutes,which illustrates it is tolerance temperature and shearing. The fracturing fluid is clean and low damage,which the filtration coefficient low,the residue content only 4.2 mg/L. It can be completely gelout and easy to return to discharge, which is beneficial to the protection of the reservoir.