The Research On The Technology Of Fracturing Fluid Through Reservoir Water

In the process of fracturing, the fracturing fluid performance plays a crucial role in increasing the oil reserves and productivity of the oil fields. Fracturing fluid is composed of the thickening agents, crosslinking agents, gel breaker, cleanup agent additives etc, which is made by clear water. Because the water resources is scarce in the area where Zibei is located and the problems arised as to the poor compatibility between the fracturing fluid formulated by clear water and the strata. High salinity formation water has favorable compatibility with stratum as well as the capability of restraining the clay expansion. However, the oil reservoir water ionic components are complex, which put forward higher request for the system of making fracturing fluid through reservoir water. The following conclusions could be drawn from the comprehensive analysis of the water in Zibei:all the water belonged to CaCl2, the total salinity topped 8.53×104mg/L, the calcium content was especially high, the suspended material content and the oil content was high. The research of influence of the components in reservoir water on fracturing fluid base fluid viscosity and crosslinking indicated that the suspended material was the leading factor which affected the base fluid viscosity. The calcium ions reacted with borax leading to precipitation and thereby affecting the corsslinking.The process of making fracturing fluid generally adopts the system in which borax is used as crosslinking agent and ammonium persulfate as gel breaking agent. From the evaluation of the system in which the fracturing fluid was made through reservoir water such aspects could be found:crosslingking with borax could lead to poor viscoelasticity if less borax was added and more borax could lead to excessive crosslinking, which rendered the system crisp and resistant to shear. Using ammonium persulfate as gel breaking agent will interact with calcium ion of reservoir water which will produce calcium sulfate scaling and damage strata. This thesis aimed at these problems and formed a complete set of system by synthesizing organic boron crosslinking agent, screening Enzyme Enz-4 as gel breaking agent and adding a little clean up additive. The new fracturing fluid system was heat-resistant, resistant to shear and gel breaking performance was fast and thorough, filtration coefficient was 3.05×10-4 m/(?) and had favorable filtration reducing performance, the sand carrying ability was good, the remains of gel breaking fluid was low and the content was 450mg/L, the damage of the matrix permeability was 22.6%, which did little harm to the stratum, the on-the-spot increasing productivity was 40.2%, thus achieving favorable effect in increasing productivity.