Optimization And Application Of The Novel Low-damage Fracturing Fluid Of Vegetable- Gum With Many Side Groups

The low permeability reservoirs in the peripheral oil fields are the main reservoirs for increasing production in Daqing fields. It must be fractured before being put into development. The formation is easy to be damage in the process of fracturing due to the poor reservoir properties and vulnerable. How to control and reduce the formation and man-made crack damage effectively during the fracturing process, and how to enhance the well productivity of this low permeability reservoir are the serious challenges we have to face. In addition, Hailar oilfield of Daqing has complex lithology and poor physical condition. Sand plug occers occasionally, even if the proppant concentration is low during the fracturing process. How to improve the success rate of fracturing treatment is the key issue which must be solved for Hailar oilfield fracturing stimulation.The structure and molecular weight of the novel vegetable gum (VG) with many side groups are characterized using IR, NMR, light scattering, viscosity and other experimental methods. The molecular structure of this novel VG is also composed of galactose and mannose unit. The ratio of side galactose groups with mannose on main chain is 1:1.34, significantly greater than ordinary guar gum with the raio of 1:1.67.The molecular weight of this novel vegetable gum is 5×105, significantly lower than the molecular weight of ordinary guar gum. The steric effect makes the rigidity of the polymer chain increase accordingly due to the reason that new VG has more side groups. As a result, the intermolecular aggregation of the novel VG chains through the hydrogen bonding is prevented. This explains why this novel VG has the better water-soluble performance and lower water insolubles so that thickening behavior is much better than ordinary guar gum.Based on this new gum, a novel fracturing fluid is developed and the performance of that is studied and compared with the hydroxypropyl guar (HPG) aqueous solution. In the conditions of the same shear viscosity and temperature, the usage amount or concentration of VG is lower than HPG by nearly 30%,and the residue content of this novel fracturing fluid is nerely 45% lower than that of HPG based fracturing fluid. Therefore, it reduces the damage of both reservoirs and man-made crack, which on the needs and satisfaction of the fracturing treatment on the low permeability reservoirs.The paper also present the criterion by which the performance of fracturing fluid can be determined by using the combination of platform modulus Gp and zero shear viscosityη0 obtained by the small oscillation shear experiments. This paper also studies the performance of this novel fracturing fluid at different crosslinker concentrations and different VG concentrations and compares it with the performance of HPG based fracturing fluid.By optimizing and selecting two different organic molecules which have different molecular sizes and different complex capacity with boron, together with controlling the reaction conditions, a novel boron based crosslinker is synthesized. The crosslinking time of fracturing fluid may be delayed and controllable due to the steric effect and sequential release technology, the performance of boron based crosslinker, including the stability, resistance to the high temperature and shear rate, enhances significantly. The pipeline friction is dropping rapidly along the fracturing process and improve the success rate of fracturing process by crosslinker with the novel VG thickener,We also optimize the overall performance of this novel VG fracturing fluid. By introducing the cationic polyelectrolyte with the low molecular weight and multi-degree of branching such as polydimethyldially ammonium chloride, the positive charges along the polymer chains can combine different clay particles, and then inhibit the clay particles form breaking, losing, and migrating. By combining surfactants of oxidation of ammonium with the surfactants containing fluorine, the surface and interface tension reduces whereas the contact angle increases signifacntly. As a result, the capillary force becomes nerely zero, improving the flowback ability and other performances of fracturing fluid significantly. In addition, in this paper we also optimized demulsifiers, fungicides, soluble fluid filtration additive, capsule breaker to endue fracturing fluid better anti-emulsifying, anti-metamorphic, lower fluid filtration and gel breaking performance.By using the novel plant gum fracturing fluids with many side groups, we carry out fracturing treatment in 1791 zones 576 wells in low permeability reservoir of daqing peripheral oilfields, the fracturing operation success rate is 97.0%, the average daily fluid production of single well in the early stage after fracturing is 3.19m3/d. Based on the novel fracturing fluid technique, the formation damage problem during fracturing process which treats on low permeability reservoirs of the peripheral oil fields of Daqing can be solved effectively.By using this novel fracturing fluid, the fracturing treatment is carried out on reservoirs which are deeply buried and have high mud content conditions in Hailaer oifield. Accumulated in 52 wells, about 89 layers, the average reservoir depth is 2634.9m, the success rate and the average liquid production is 96.6% and 10.84 m3/d respectively. Base on the contrast testing with the bottom-hole pressure device, the results show that by using the delayed crosslinking fracturing technique, the pipeline friction of fracturing fluid reduces at least 5.7 Mpa. Without changing the conditions of fracturing equipments on the ground,the sand plug during fracturing treatment process with low proppant concentrations and even the failure to fracturing the reservior can be solved. The success ratio of fracturing increases from about 80% in the past to at least 96% at present. Based on the novel fracturing fluid technique, the success rate of fracturing treatment on high mud content reservoirs in Hailaer oil field can be improved effectively. So far, a number of wells are treated by this novel VG based fracturing fluid is 628, about 1808 layers .The success rate is up to 96.96%. The average well productivity is 2.65t/d. The efficiency of the production enhancement treated by this fracturing fluid is 1.33 times higher than that treated by conventional HPG based fracturing fluid. The application of this new technology will reduce formation damage due to fracturing fluid filtration and improve fracturing stimulation effect and economic benefits significantly, which have met the needs of developing low permeability oil fields.