Method for determining unsteady flow bottom hole pressure of fractured well in dense oil reservoir

Abstract

The invention proposes a method for determining unsteady flow bottom hole pressure of a fractured well in a dense oil reservoir. The method comprises the following steps of hydraulically fracturing areservoir to form a vertical well with multiple fractures; collecting fracture parameters of the multiple fractures and basic information of the oil reservoir, wherein the fracture parameters includefracture orientation and permeability; establishing a multi-fracture physical model for the fracturing vertical well; in the multi-fracture physical model, determining a dimensionless bottom hole pressure calculation equation based on the permeability and fracture orientation for a single fracture; determining a change value of the bottom hole pressure of a single fracture along with the time in combination with the fracture parameters and the basic information of the oil reservoir according to the dimensionless bottom hole pressure calculation equation; and repeating the above steps to calculate change values of the bottom hole pressure of each fracture in the multiple fractures along with the time. The method provided by the invention has the advantages of comprehensively considering thedense oil reservoir geology and the static parameters of the oil reservoir itself, considering the influence of asymmetric distribution of the fractures on the wellbore at the same time, and perfecting the description of a bottom hole fluid flow model of the fractured well.

Description

technical field [0001] The invention relates to the field of oil and gas well development, in particular to a method for determining the bottom hole pressure of a fracturing well in a tight oil reservoir with unsteady flow. Background technique [0002] Since tight oil reservoirs are characterized by low porosity, low permeability, and extremely poor oil content, the effect of early water injection development is not ideal, and development is very difficult. Therefore, in order to establish a favorable channel for reservoir fluid, To improve development efficiency, hydraulic fracturing is generally used to open the reservoir, and then supplement the energy of the formation according to the characteristics of the reservoir in the later stage. With the development of tight oil reservoirs, the requirements for the accuracy of subsurface seepage models are getting higher and higher, and the complexity of production well processing is getting higher and higher, which will make it...

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Problems solved by technology

[0004] 1. The measurement of the liquid level is inaccurate, mainly due to the poor effect of the test instrument and the existence of foam;

[0005] 2. The density value is inaccurate. Generally, the density measured under ground experimental conditions is used as the reference value. This is also one of the reasons for the calculation error, mainly because the fluid in the wellbore is not single-phase, and the flow form is also relatively complicated. Therefore, it is not possible to simply rely on single-phase steady-state flow to measure fluid density;

[0006] 3. The water cut test is inaccurate. The current models assume that the water cut during continuous flow is equivalent to the water cut (surface) before and after the test, but in fact, when the oil well is shut in, the components in the wellbore will follow the bottom hole pressure. Changes occur, and the water-oil ratio of the underground and the ground is also different;

[0007] 4. The calculation model is too single, simple and idealized

Although this patent considers the fluid coupling among fractures, reservoirs and wellbore, in the second step of the patent implementation, that is, in the process of establishing the productivity equation, the fracture is directly treated as symmetrical about the wellbore center

Although the solution process is simplified, the fractures formed by hydraulic fracturing are not necessarily symmetrical about the wellbore center, and the distribution of fractures is random. Therefore, simply treating the fractures as symmetrical about the wellbore has some discrepancies with the actual fracture distribution. Therefore, this patent does not solve the influence of fracture orientation on bottom hole pressure

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