Small fracturing test method suitable for shale gas well

Abstract

The invention provides a small fracturing test method suitable for a shale gas well. The method comprises the following steps that (1) acid pretreatment is conducted, (2) the stable injection time and liquid quantity of the highest discharging quantity are determined; (3) step increasing is conducted, specifically, the discharging quantity is gradually increased to the highest discharging quantity in a stepped mode; (4) step decreasing is conducted, specifically, the discharging quantity is gradually decreased from the highest discharging quantity in a stepped mode; and (5) pressure decreasing testing is conducted, specifically, after fracturing pumping stopping, pumping stopping and well shutdown are conducted for a preset time till an inflection point appears at the pressure decreasing curve. According to the small fracturing test method suitable for the shale gas well, key characteristic parameters, such as the minimum horizontal principal stress, the fracture closure time, the natural fracture development degree and the stratum leak-off condition, of a shale formation can be obtained, the effect of fractural diverting inducing is achieved, a foundation is laid for fractural diverting or complex fracture forming in main fracturing, the transformation size of main fracturing is increased, and the fracturing effect of main fracturing is improved. The small fracturing test method is reasonable in design, simple in technique and convenient to operate.

Description

Technical field [0001] The invention relates to the field of shale reservoir fracturing stimulation and improvement, and more particularly to a small-scale test fracturing method suitable for shale gas wells. Background technique [0002] At present, the practice of testing fracturing in shale gas usually adopts the method in conventional sandstone, but on a slightly larger scale. However, due to the particularity and complexity of shale gas and conventional sandstone gas, the design method of conventional test fracturing mainly has the following problems: [0003] 1) Since the shale is not swelling and breaking through infiltration, but bending and deforming, the conventional step-up displacement design, especially the multi-step-up mode, needs to be improved; [0004] 2) Due to the relatively developed horizontal bedding joints / texture joints of shale, if the initial displacement design is too small, it will be difficult to pass through the first bedding joints / texture joints even...

AI Technical Summary

Problems solved by technology

[0003] 1) Since the shale is not broken by imbibition but broken by bending deformation, the conventional step-up displacement design, especially the multi-step step-up model needs to be improved;

[0004] 2) Since the horizontal bedding fractures / texture fractures of shale are relatively developed, if the initial displacement design is too small, it will be difficult to pass through the first bedding fractures / texture fractures even with high displacement;

[0005] 3) In particular, the wellbore blockage in the first stage of fracturing in horizontal wells is serious. In the past, test fracturing was generally performed without acidizing pretreatment, which would cause certain illusions and interference effects in the interpretation of formation characteristics;

[0006] 4) The duration of the highest stepped displacement is relatively short. First, the probability of fractures encountering natural fractures is reduced. Second, the fluid volume in this section determines the scale of the entire testing fluid used for fracturing. If the fluid volume is small, the induced The stress is small, and the effect on the change of the stress field near the fracture (the two-dimensional horizontal stress tends to be uniform) is not obvious, resulting in a significant reduction in the complexity of the fracture or the probability of fracture diversion during the main fracturing;

Due to the extremely low permeability of the shale matrix, unless the interconnected natural fractures or bedding fractures / texture fractures are continuously connected, the shut-down time of the pump and the well is too short, and the fractures may be far from reaching the closure time, which brings great difficulties to fracture interpretation. big difficulty