CN-116950626-B - Method for evaluating mechanism of improving fluidity of thickened oil by thermochemical flooding

CN116950626BCN 116950626 BCN116950626 BCN 116950626BCN-116950626-B

Abstract

The invention discloses a method for evaluating a mechanism for improving flowability of thick oil by thermochemical flooding, which comprises the steps of carrying out a first experiment of saturating a target layer thick oil on an experiment rock core according to a speed experiment group containing different injection speed parameters to obtain a first outflow volume and a first pressure difference under different injection speeds, carrying out a second experiment of displacing the target layer thick oil on the thermochemical system of the target layer on the experiment rock core according to the speed experiment group to obtain a second outflow volume and a second pressure difference under different injection speeds, determining a displacement starting pressure gradient and a flow index difference according to the first outflow volume and the first pressure difference under different injection speeds and the second outflow volume and the second pressure difference under different injection speeds, and determining an effective displacement mechanism at the position of the target layer of the experiment rock core through the change states of the displacement starting pressure gradient and the flow index difference. The invention forms a flow for quantitatively evaluating the mechanism of improving the recovery ratio of the heavy oil by thermochemical flooding for heavy oil reservoirs in different areas.

Inventors

SHANG GENHUA
ZHANG YONGQING
CUI SHUYUE
LI XIAOBO
LIU KUNYAN
LIU HONGGUANG
SHANG RUYUAN
CHENG SHIQING
ZHENG SONGQING
WANG QIANG
GU HAO
LIU HAILONG
TAN TAO
LI YONGQIANG

Assignees

中国石油化工股份有限公司
中国石油化工股份有限公司石油勘探开发研究院

Dates

Publication Date: 20260508
Application Date: 20220414

Claims (6)

1. A method for evaluating a mechanism of thermochemical flooding to improve the mobility of thick oil comprising: According to a speed experiment group containing different injection speed parameters, carrying out a first experiment of the saturated target layer thick oil on an experiment core to obtain a first outflow volume and a first pressure difference at different injection speeds; According to the speed experiment group, carrying out a second experiment of displacing the thick oil of the target layer by using a thermochemical system of the target layer on the experiment core to obtain a second outflow volume and a second pressure difference at different injection speeds; Determining a displacement start pressure gradient and a flow index difference according to the first outflow volume and the first pressure difference at the different injection speeds and the second outflow volume and the second pressure difference at the different injection speeds; determining an effective displacement mechanism at a destination layer position of the experimental core through the displacement start pressure gradient and the change state of the flow index difference value, wherein the effective displacement mechanism comprises the following steps: Comparing the displacement start pressure gradient and the flow index difference value with zero values respectively, and determining a corresponding effective displacement mechanism according to the comparison result, wherein the effective displacement mechanism is selected from one of start pressure reduction, crude oil viscosity reduction and interfacial tension reduction, and the effective displacement mechanism comprises the following steps: Determining an effective displacement mechanism at a destination layer position of a current experimental core as a reduced starting pressure when the displacement starting pressure gradient is greater than zero and the flow index difference is about zero; Determining an effective displacement mechanism at a target layer location of the current experimental core as reducing the viscosity of the crude oil when the displacement initiation pressure gradient is about zero and the flow index difference is greater than zero; and determining an effective displacement mechanism at the target layer position of the current experimental core as reducing the interfacial tension when the displacement start pressure gradient is greater than zero and the flow index difference is greater than zero.
2. The method of claim 1, wherein in the step of determining a displacement initiation pressure gradient and a flow index difference from a first outflow volume and a first pressure differential at the different injection rates and a second outflow volume and a second pressure differential at the different injection rates, comprising: nonlinear fitting is carried out on the first outflow volume and the first pressure difference at different injection speeds, and a flow characteristic curve of thick oil of a target layer is drawn, so that a first starting pressure and a first nonlinear flow index of the thick oil of the target layer are obtained; Non-linearly fitting the second outflow volume and the second pressure difference at the different injection speeds, and drawing a flow characteristic curve about the thermochemical displacement process, thereby obtaining a second starting pressure and a second non-linear flow index of the displacement fluid system; and obtaining the displacement starting pressure gradient according to the first starting pressure and the second starting pressure, and obtaining the flow index difference value according to the first nonlinear flow index and the second nonlinear flow index.
3. The method according to claim 1 or 2, characterized in that in the second experiment the injection amount ratio of the thick oil of the destination to the thermochemical system of the destination is 1:10.
4. The method according to claim 1 or 2, characterized in that the method further comprises: And obtaining the displacement starting pressure gradient and the flow index difference value corresponding to the experimental rock cores at different positions in the target area, calculating the duty ratio of various effective displacement mechanisms in the target area, and determining the effective displacement mechanism required to be adopted by the current target area in the current stage based on the duty ratio.
5. The method of claim 4, wherein the step of determining the position of the first electrode is performed, And respectively carrying out normalization processing on the displacement start pressure gradient and the flow index difference value corresponding to each experimental core, calculating the duty ratio and determining a main displacement mechanism to be adopted in the next stage by analyzing the change of normalized displacement start pressure gradient data and normalized flow index difference value data.
6. A method according to claim 1 or 2, characterized in that, Respectively carrying out a plurality of rounds of first experiments at different injection speeds, and recording core outlet flow velocity average value and core inlet and outlet pressure difference average value which correspond to each round of first experiments when core outlet pressure and flow reach a steady state in the process of each round of first experiments, so as to obtain first outflow volume and first pressure difference at the different injection speeds; And respectively carrying out a plurality of rounds of second experiments at different injection speeds, and recording that core outlet pressure and flow reach corresponding core outlet flow velocity average value and core inlet and outlet pressure difference average value under a stable state in the second experiment process of each round, so as to obtain second outflow volume and second pressure difference at different injection speeds.

Description

Method for evaluating mechanism of improving fluidity of thickened oil by thermochemical flooding Technical Field The invention relates to the technical field of deep-layer broken-solution heavy oil reservoir development, in particular to a method for evaluating a mechanism of improving heavy oil fluidity by thermochemical flooding. Background High viscosity Heavy crude Oil is internationally called Heavy Oil (Heavy Oil), and is commonly called Heavy Oil in China, namely crude Oil with the viscosity of more than 50mPa.s and the density of more than 0.92g/cm3 under the condition of an Oil layer. For very heavy crude oils with a crude oil viscosity greater than 10000mpa.s and a crude oil density greater than 0.98g/cm3, it is referred to as natural bitumen or tar sands oil. The world thick oil reserves are quite abundant, which is about 15-20% of the world oil reserves, the Chinese thick oil resources are abundant, the reserves are huge, the distribution range is wide, wherein the thick oil reserves of Bohai sea oil fields, liaohe oil fields, victory oil fields, henan oil fields and Xinjiang oil fields are considerable. Taking Bohai sea oil field as an example, the thickened oil resource accounts for 75% of the total resource, and the accumulated accumulation finds that the three-level thickened oil has a geological reserve of 23.18 hundred million tons, the unused reserve is about 13.15 hundred million tons, the occupied ratio is 56.7%, the overall recovery ratio is low, the residual oil distribution is wide, and the development potential is huge. Whether it is a sandstone oil reservoir or a carbonate oil reservoir, since the heavy oil has the characteristics of high heavy component content, large viscosity, poor fluidity and the like, the economic yield is difficult to obtain by utilizing the conventional exploitation means, and other measures must be taken to realize the efficient development of the heavy oil reservoir. Common thick oil development measures are thermal recovery and chemical methods. The thermal recovery technology comprises steam throughput, steam flooding, SAGD, fire layer and the like, and the chemical agent method comprises chemical flooding, polymer flooding, binary compound flooding, ternary compound flooding, foam flooding and the like. The technology has respective application conditions and development advantages and also has various disadvantages no matter the technology is thermal recovery technology or chemical agent oil displacement technology. Thermal recovery of heavy oil often results in vapor gravity overburden and fingering due to differences in oil and vapor density and viscosity, resulting in a reduction in vapor recovery volume sweep efficiency. On the other hand, in the steam sweep area, most of the thickened oil cannot be stripped from the rock surface due to the influence of the interface characteristics of the rock-crude oil-water system, and the final recovery ratio is reduced. Compared with sandstone heavy oil reservoirs, the maximum difference between the heavy oil reservoirs in northwest China petrochemical oil fields and eastern heavy oil reservoirs is influenced by deep fracture, the difference of the flow properties of crude oil in the longitudinal direction is much larger, and the situation is far different from the problem that the flow properties of the eastern heavy oil reservoirs are only poor in a shaft, namely, the difference of the flow properties of deep-layer broken solution heavy oil reservoirs exists in the shaft and the oil reservoirs. Meanwhile, because of large oil reservoir burial depth and huge shaft heat loss, the conventional method for improving the flow property and recovery ratio of the heavy oil by injecting hot water or hot steam is not suitable, the effect is poor, and the flow property of the heavy oil is improved by adopting the cooperation of a chemical method and a hot water method in a field plan, so that the recovery ratio of the heavy oil reservoir is improved. The difficulty of the development of the heavy oil reservoir is that the viscosity of the crude oil is reduced as much as possible, the flow capacity of the crude oil reservoir is improved, the fluidity ratio of the injected fluid is improved, the interfacial tension between the injected fluid and the crude oil is reduced, and the oil displacement efficiency and the sweep degree are improved. The traditional thermal recovery mode can reduce the viscosity of the thickened oil and improve the fluidity of the crude oil, but the phenomena of steam channeling, rapid increase of water content and the like are easy to occur along with the deepening of the thermal recovery degree. On the other hand, the oil displacement is carried out by simply utilizing the chemical agent, so that the development cost is greatly increased, and the efficient development of the oil field is restricted. Based on the two aspects, a novel technology for improving the flow performance of the thickened