CN-121993184-A - Multi-crack near-well characteristic evaluation system and method

CN121993184ACN 121993184 ACN121993184 ACN 121993184ACN-121993184-A

Abstract

The invention discloses a multi-crack near-well characteristic evaluation system and a multi-crack near-well characteristic evaluation method, which belong to the technical field of hydraulic fracturing and comprise a shaft divided into N+1 sections, N cracks in the shaft, a well head excitation device, a pipeline with the shaft being approximately one-dimensional and equal in cross section, pipe waves propagating in the shaft at a constant speed, and numbering all key nodes in the shaft, wherein the well head excitation device is arranged at the end of the well head and provides high-frequency pipe waves for the well head. According to the technical scheme, the existing single-fracture model is improved, the multi-fracture condition in the shaft is specifically analyzed and calculated, a time-course curve of pressure and flow at any position of the shaft is obtained, parameters of fracturing fracture are obtained, the requirement of high-frequency tube wave diagnosis is met, and the technical problem that the multi-cluster fracture is approximate to single fracture treatment in the prior art, and the near-well characteristics of the multi-fracture are difficult to evaluate is solved.

Inventors

GONG WEI
LI DAN
HE LE
GUAN BIN
WANG SUBING
ZHAN LI
QU JIANFENG
WANG RONG
ZHU JUHUI
ZHANG JUNCHENG

Assignees

中国石油天然气集团有限公司
中国石油集团川庆钻探工程有限公司

Dates

Publication Date: 20260508
Application Date: 20241104

Claims (10)

1. The multi-fracture near-well characteristic evaluation system is characterized by comprising a well bore divided into N+1 sections, N fractures in the well bore and a wellhead excitation device; The well bore is approximately a one-dimensional pipeline with the same cross section, pipe waves propagate in the well bore at a constant speed, and each key node in the well bore is numbered, wherein the number of the well head node is i=0, each crack is sequentially numbered i=1 and 2. The wellhead excitation device is arranged at the wellhead end and provides high-frequency pipe waves for the wellhead.
2. The multi-fracture near-well characteristic evaluation system according to claim 1, wherein the fluid exchange control equation at the fracture in the wellbore is set to: Wherein p is pressure, Q is wellbore fluid flow, z is well depth, t is time, A T is wellbore cross-sectional area, K is compression modulus of fluid, ρ is fluid density, z i is well depth of ith fracture, Is the flow rate from the wellbore into the fracture i.
3. The multi-fracture near-well characteristic evaluation system according to claim 2, wherein: Wherein: Is the cross-sectional area of the hydraulic connection of fracture i to the wellbore.
4. The multi-fracture near-well characteristic evaluation system of claim 3, wherein: Where c is the velocity of tube wave propagation, K is the compressive modulus of the fluid and ρ is the fluid density.
5. The multi-fracture near-well characteristic evaluation system according to claim 4, wherein the fracture boundary conditions at each fracture comprise: Pressure is continuous: Conservation of flow:
6. the method for multi-fracture near-well characteristic evaluation according to any one of claims 1-5, comprising the steps of: Step S1, establishing 2N+2 linear equation sets based on the well bore boundary range, the fluid exchange control equation at the crack in the well bore and the boundary conditions at the wellhead and the bottom hole bridge plug to solve 2N+2 unknown quantities Is a characteristic variable of a pipe wave propagating in positive and negative directions in a shaft Wherein omega is the angular frequency and z i is the well depth of the ith fracture; S2, after the solving is completed, calculating the pressure and the flow at any position in the shaft by utilizing the characteristic variables of the pipe waves propagating in the positive and negative directions in the shaft; And step S3, defining function Fourier transformation and inverse transformation, and obtaining a time-course curve of pressure and flow at any position of the shaft by using the inverse discrete Fourier transformation.
7. The method for evaluating multi-fracture near-well characteristics according to claim 6, wherein the step S1 specifically comprises the following sub-steps: Step S11, defining characteristic variables Q ± , wherein the characteristic variables respectively represent pipe waves propagating in +z and-Z directions, and Q ± ＝p±Z T Q, wherein p is pressure, Q is wellbore fluid flow, and Z T is hydraulic impedance of the pipe waves; Step S12, defining a shaft between Z epsilon (Z i ,z i+1 ), wherein characteristic variables propagating in positive and negative directions are respectively expressed as: wherein Z is well depth, omega is angular frequency, For imaginary number, c is the velocity of pipe wave propagation, z is the well depth, z i is the well depth of the ith fracture; step S13, defining phase coefficient Where i=0, 1,2,..n, g i represents the phase change during the propagation of a tube wave from Z i to Z i+1 , defined separately according to the phase coefficients And Pressure and flow rate: Wherein omega is the angular frequency of the wave, C is the velocity of tube wave propagation; Step S14, the pressure intensity at the crack opening is reduced Flow into the fracture Model coupling along a fracture by fluid Wherein the method comprises the steps of For fracture hydraulic impedance, rewriting the flow conservation equation according to the coupling formula is: step S15, substituting the pressure and flow formula calculated in the step S13 into the rewritten flow conservation equation to obtain: Wherein, the The ratio of the hydraulic impedance of the pipe wave to the i fracture; Step S16, designating pressure and flow by utilizing boundary conditions at a wellhead and a well bottom bridge plug, and defining the reflection coefficient of the flow as follows: Wherein, r b = -1 corresponds to a completely closed bottom hole, the flow is 0, and r b = 1 corresponds to a bottom hole pressure variation of 0.
8. The method for multi-fracture near-well characteristic evaluation according to claim 7, wherein in the step S16, the specifying the pressure and the flow rate using boundary conditions at the wellhead and the bottom hole bridge plug is specifically: Pressure intensity: Flow rate:
9. The method for multi-fracture near-well characteristic evaluation according to claim 8, wherein the step S2 of pressure and flow specifically comprises: The solution of pressure and flow in the pipeline is obtained by utilizing the characteristic variables of pipe waves propagating in +z and-z directions and the characteristic variables propagating in positive and negative directions of a shaft between z epsilon (z i ,z i+1 ): the solution of pressure and flow rate in the (z i-1 ,z i ) section is:
10. The method for multi-fracture near-well characteristic evaluation according to claim 9, wherein the step S3 fourier transform specifically comprises: Defining a function fourier transform and an inverse transform: where ω is the angular frequency and, Is an imaginary number; In a continuous wellbore section between fractures, homogeneous equations defining the characteristic variables are: fourier transforming the homogeneous equation of the characteristic variable: The method comprises the following steps:

Description

Multi-crack near-well characteristic evaluation system and method Technical Field The invention relates to the technical field of hydraulic fracturing, in particular to a multi-crack near-well characteristic evaluation system and method. Background The hydraulic fracturing technology can obviously improve the permeability of compact unconventional oil and gas fields, and is a key technology for development of unconventional oil and gas resources. At present, although drilling precision technology is greatly developed, the geometric dimension and conductivity evaluation means of hydraulic fracture are still very limited, and challenges are provided for optimizing well completion and production. The tubing wave is an interfacial wave propagating along the fluid filled wellbore, has sufficient energy in the fluid and the elastic medium near the wellbore (Biot, 1952), is sensitive to well Zhou Yanceng and fracture parameters, and is therefore widely used in logging techniques, and propagates down the fluid filled wellbore after the wellhead is shut in by pumping or active seismic excitation, and reflects at the juncture of the hydraulic fracture and the wellbore, where the arrival time and waveform of the transmitted signal contain fracture location and near-well characteristics such as width, length and permeability. When the fracture is completely filled with fluid, krauklis waves (also known as fracture waves) may form that propagate along the fracture, particularly sensitive to the geometry of the fracture. In practice, the artificial fracture tends to be filled with propping agent quickly after fracturing, but because low-frequency signals (1-10 Hz, with the wavelength of 150-1500 m) are mainly adopted, in the prior art, the pressure at the outlets of all the fracture clusters in the same fracturing stage is assumed to be equal, and the multi-cluster fracture is approximate to a single fracture treatment, so that the near-well characteristics of the multi-fracture are difficult to evaluate. Disclosure of Invention The invention aims to solve the problems in the prior art, provides a multi-fracture near-well characteristic evaluation system and a multi-fracture near-well characteristic evaluation method, improves the existing mode of approximating multi-cluster fractures to single fracture treatment, and accurately evaluates the multi-fracture characteristics. The invention aims at realizing the following technical scheme: the multi-fracture near-well characteristic evaluation system comprises a well bore divided into N+1 sections, N fractures in the well bore, and a wellhead excitation device; The well bore is approximately a one-dimensional pipeline with the same cross section, pipe waves propagate in the well bore at a constant speed, and each key node in the well bore is numbered, wherein the number of the well head node is i=0, each crack is sequentially numbered i=1 and 2. The wellhead excitation device is arranged at the wellhead end and provides high-frequency pipe waves for the wellhead. Preferably, the fluid exchange control equation at the fracture in the wellbore is set to: Wherein p is pressure, Q is wellbore fluid flow, z is well depth, t is time, A T is wellbore cross-sectional area, K is compression modulus of fluid, ρ is fluid density, z i is well depth of ith fracture, Is the flow rate from the wellbore into the fracture i. Preferably, the method comprises the steps of, Wherein: Is the cross-sectional area of the hydraulic connection of fracture i to the wellbore. Preferably, the method comprises the steps of, Where c is the velocity of tube wave propagation, K is the compressive modulus of the fluid and ρ is the fluid density. Preferably, the crack boundary conditions at each crack include: Pressure is continuous: Conservation of flow: the method for evaluating the multi-fracture near-well characteristics comprises the following steps: Step S1, establishing 2N+2 linear equation sets based on the well bore boundary range, the fluid exchange control equation at the crack in the well bore and the boundary conditions at the wellhead and the bottom hole bridge plug to solve 2N+2 unknown quantities Is a characteristic variable of a pipe wave propagating in positive and negative directions in a shaftWherein omega is the angular frequency, and Z i is the well depth of the ith fracture; S2, after the solving is completed, calculating the pressure and the flow at any position in the shaft by utilizing the characteristic variables of the pipe waves propagating in the positive and negative directions in the shaft; And step S3, defining function Fourier transformation and inverse transformation, and obtaining a time-course curve of pressure and flow at any position of the shaft by using the inverse discrete Fourier transformation. Preferably, the step S1 specifically includes the following substeps: Step S11, defining characteristic variables Q ±, wherein the characteristic variables respectively repr