(1. China Petroleum Exploration and Development Research Institute, Beijing100083; China Youshi University (Beijing), Beijing102249; 3. Yangtze University, Jingzhou 434023)
The dynamic damage evaluation system of high temperature and high pressure cores is a new experimental method and instrument for evaluating the depth and degree of reservoir damage in petroleum exploration and development. It can measure the original permeability of each section before the cores are damaged by the fluid entering the well, and then under the simulated reservoir temperature, pressure and flow rate conditions, the fluid entering the well is directly displaced into the high pressure liquid tank by a mud pump to dynamically shear the core end face. After the damage process is completed, it is not necessary to take out the core, but to change the flow direction of the fluid through the reversing valve, and then to displace the liquid with the advection pump to measure the permeability of each section of the damaged reservoir core. By comparing the permeability changes of each section of the core, the depth and degree of damage to the core by the fluid entering the well can be determined, so as to optimize the drilling fluid and completion fluid that meet the needs of protecting oil and gas reservoirs. At present, the "evaluation system" and its supporting intelligent software have been put into use in many oilfield enterprises and achieved good application results.
Dynamic damage evaluation system for core reservoir protection; Drilling fluid and completion fluid
A New Method for Evaluating Formation Damage Caused by Drilling and Completion Fluid —— Research on ——HTHP Core Dynamic Damage Evaluation and Testing System
Yu Wei-Chu 1, 2, 3,-Ming 1,-year 2.
(1. Sinopec Petroleum Exploration and Development Research Institute, Beijing100083; 2. China Shiyou University, Beijing102249; 3. Yangtze University, Jingzhou 434023)
HTHP core dynamic damage evaluation and testing system is a newly developed new method and instrument for evaluating the formation damage caused by drilling and completion fluid in petroleum exploration and development. It can be used to measure the original permeability of each part of the core sample before it is polluted by drilling fluid or completion fluid. Then, without taking out the core, the dynamic damage process can be directly carried out under the simulated formation temperature, pressure and flow conditions by flushing with drilling fluid or completion fluid with mud pump. After the damage process is completed, the core is still kept in the holder, and the permeability of each part of the damaged core sample can be measured by changing the flow direction with a reversing valve and flushing the fluid (clean water or kerosene) with a constant flow pump. By comparing the permeability data of each section of core samples, the damage degree and invasion depth can be determined, and the drilling fluid and completion fluid that meet the requirements of formation protection can be selected. At present, the new evaluation method, testing system and supporting software of formation damage caused by drilling fluid and completion fluid have been widely used in many oil fields and achieved good results.
Core protection; Dynamic damage testing system; Drilling and completion fluid
With the continuous expansion and development of world oil production, reservoir damage and protection are increasingly concerned by petroleum engineers all over the world. Once reservoir damage occurs, its remedial measures need to pay a high price. Therefore, as early as 1940s-1950s, laboratory experiments on reservoir damage and protection began abroad. In 1970s and 1980s, China began to study the problem of reservoir damage, and established corresponding experimental methods and related instruments for reservoir damage evaluation. However, with the exploration and development of oil and gas fields gradually turning to deep layers, the original reservoir damage evaluation method can no longer adapt. Therefore, in order to achieve a breakthrough in the technical field of oil and gas reservoir protection, it is necessary to establish a complete set of new methods and supporting evaluation means for reservoir damage evaluation, which can not only measure the original permeability and damage permeability of each section of the core, but also simulate the conditions such as reservoir temperature, pressure and mud return rate to evaluate the dynamic damage of the core.
This paper mainly introduces its design idea, design principle, technical performance index, calculation method of experimental parameters and its application.
1 Design idea and working principle of "evaluation system"
Design idea of 1. 1
(1) The "evaluation system" should first be able to measure the original permeability (Koi) and damage permeability (Kdi) of each section of the core. According to the working principle and design idea of the patented technology permeability gradiometer (patent number: 9 1226407 438+0) of this project team, the permeability parameters of each section of the core before and after damage can be easily calculated by using Darcy theorem formula.
(2) According to the working principle and design idea of a new intelligent high-temperature and high-pressure core dynamic water loss instrument (patent number: ZL2004200 17823.7) patented by the project team, a dynamic shear pollution damage experiment was carried out on one end face of the core under the condition of simulating the temperature, pressure and mud return of the borehole annulus.
(3) According to the experimental instrument for dynamic damage evaluation of high temperature and high pressure cores (patent number: 2004 10030637. 1, ZL200420047524.8) patented by the project team, after the permeability measurement is completed, it is not necessary to take out the cores, but to make dynamic performance under the conditions of simulating the formation temperature, pressure and mud return speed in the borehole annulus. When the core is damaged dynamically, the multi-section permeability measuring mechanism of the core is closed by using relevant valves, and the end face of the core is subjected to dynamic shear pollution by using a special mud pump under the conditions of simulating formation temperature, pressure and rising speed of mud in the borehole annulus, and the end face cyclic shear structure is adopted for dynamic pollution. By loading the core at one time and simulating the temperature, pressure and mud return rate of the borehole annulus, the core was dynamically polluted and several permeability parameters of the core before and after pollution were evaluated.
(4) In the process of multi-stage permeability test, the important part of the "evaluation system" used the patented technology of high-pressure precision advection pump (patent number: ZL02278357. 1) of this project group for the first time, and realized the constant current, constant pressure and pulse-free micro-liquid transportation technology.
(5) The core part of the "evaluation system" adopts the patented technology of the core holder of the project team (patent number: ZL932 16048.4). For the first time, the metal skeleton vulcanization technology, O-ring technology and rubber self-sealing principle were adopted, which broke the extrusion sealing structure of the old product and successfully established the multi-measuring point technology along the mandrel.
An outstanding feature of this "evaluation system" is that it organically combines the permeability change test of each section before and after core damage with the dynamic pollution damage mechanism of core end face, and successfully achieves the design purpose.
Composition and working principle of 1.2 instrument
In order to complete the multi-stage permeability test of cores on the same instrument, simulate the dynamic damage to cores under downhole conditions, and thus accurately and efficiently evaluate the effect of drilling fluid on protecting oil and gas reservoirs, according to the drilling technical requirements and the above design ideas, the design flow of the dynamic damage evaluation system for high temperature and high pressure cores is shown in Figure 1. It mainly consists of a precise advection pump, a mud pump, a liquid tank, a dynamic end circulation multi-pressure measuring point core holder, a flowmeter, an electronic balance, an air source, a pressure sensor, a temperature sensor, an annular pressure pump, a back pressure controller, a heating system, a data acquisition and processing system and the like.
Figure 1 Flow chart of dynamic damage assessment system for high temperature and high pressure cores
1- air source; 2- High pressure safety valve; 3- High pressure liquid tank; 4— Mud pump; 5— Flowmeter; 6- Electronic balance; 7— Back pressure controller; 8— Annular pressure pump; 9— End-face circulating multi-point core holder; 10- valve; 1 1- pressure sensor; 12- precision advection pump; 13- drain valve; 14- data collector; 15-data processing system (computer, printer); 16- heater
Its main working principle is: when the mud pump and related valves are closed, the permeability before and after core damage can be tested by the displacement of precision advection pump; When the mud pump, fluid pipeline and related valves are opened, the drilling fluid or completion fluid in the liquid tank can circulate under the actual reservoir conditions, so as to realize the dynamic damage simulation of the reservoir core end face. The software interface is displayed in the upper right corner of Figure 2.
The "evaluation system" consists of two parts: dynamic damage simulation system in drilling process and multi-stage permeability test system. In the dynamic damage simulation system (as shown in the left part of Figure 2), the nitrogen cylinder pressurizes the mud tank, the mud circulation pump controls the flow rate, so that the drilling fluid is pumped out of the mud tank at a certain pressure and flow rate, the core end face contacts with the core holder, and the high-temperature and high-pressure dynamic damage evaluation experiment is carried out on the core end face, and finally it flows back to the mud tank to form a closed cycle. Under the pressure, the liquid in the mud is filtered through the core, and its dynamic water loss flows to the electronic balance through the pipeline for weighing, so that many experimental parameters such as the dynamic water loss rate of the core can be measured.
In the permeability test part (as shown in the right part of Figure 2), the precision advection pump drives the experimental liquid into the core and flows to the electronic balance through the core. In addition, multiple pressure sensors collect the pressure values of each pressure measuring point of the core in real time, and then calculate the permeability parameters of each section before and after core damage according to Darcy's theorem.
Fig. 2 Software Interface of Dynamic Damage Assessment System for HTHP Core
1.3 data acquisition and control principle
The general idea of hardware design of 1.3. 1
The hardware design of the control part of the "evaluation system" should have the following main functions: ① temperature control, simulating underground high temperature working conditions; (2) Flow control, which can accurately control the displacement of the magnetic pump according to the set flow value, so as to control the drilling fluid flow at the end face of the core, so as to simulate the actual mud annular return speed during drilling operation; ③ Monitoring of confining pressure: the confining pressure of the core holder is controlled by a stepping motor, and the instrument can automatically control and monitor the pressure according to the set value and display it on the man-machine interface in real time; (4) Monitoring the working pressure of the instrument. The working pressure of the mud circulation is regulated by the air source, and at the same time, affected by the mud temperature, the software instrument automatically detects the pressure parameters; ⑤ The determination of dynamic filtration, whether the damage of drilling fluid to the core has been completed mainly depends on the dynamic filtration. When the damage is sufficient, the dynamic filtration rate curve rises to equilibrium, and it does not change or changes little, indicating that the dynamic damage experiment of drilling fluid to the core has been completed, which generally takes 150min, and so does the dynamic filtration rate of filter paper.
1.3.2 software part
The human-computer interaction, data processing and other functions of the evaluation system control software are completed by PC, which provides users with an operation management platform with good real-time, strong stability, intuitive interface and convenient use with its powerful drawing and data processing functions. Users can clearly grasp the operation of the whole instrument through computer software, adjust the parameters in the experiment process conveniently and timely, and analyze the data. It provides a friendly and convenient human-computer interaction interface and data processing environment for researchers, and realizes the functions of data storage, experimental curve drawing, data report output and historical data query, including experimental parameters such as pore volume multiple of fluid passing through the core, permeability of each section of the core, permeability damage rate, permeability recovery rate, dynamic filtration rate of drilling fluid and completion fluid passing through the core, etc. The experimental data report is directly printed by the computer, and the "evaluation system" control software.
1.4 main technical indicators
The main technical performance indexes of this "evaluation system" are as follows: (1) Pollution pressure of drilling fluid and completion fluid: 0 ~ 10 MPa, and the measured maximum flowing pressure of core permeability can reach 60 MPa；; ; (2) Working temperature: room temperature ~ 150℃ (maximum 230℃); (3) The linear velocity of the fluid at the end of the core: 0 ~1.8m/s; (4) Experimental core specification: artificial or natural reservoir core with the size of φ 25× 25-90; (5) Pressure measurement accuracy: 2 ‰; (6) Drilling fluid dosage: 2 ~ 3L；; (7) Permeability measurement range: (1~ 5000) ×10-3 μ m2; (8) Power supply: 220V, 50Hz (regulated power supply is required).
Compared with other experimental devices for reservoir damage evaluation, the "evaluation system" has obvious advantages in working pressure and temperature, core permeability measurement range and so on. It is not difficult to see that it is suitable for all kinds of permeable reservoirs, abnormal high pressure or abnormal low pressure reservoirs, and also for deep wells with bottom hole temperature exceeding 150℃.
2 experimental parameters and calculation methods
2. Calculation of1v return
During drilling, the annular return velocity at the drill pipe and drill collar can be calculated by the following formula:
Oil and gas accumulation theory and exploration and development technology
Where: q is the displacement of mud pump at the drilling site (liter/second); D 1, r is the diameter and radius (in) of the drill bit respectively; D2 and r are the diameter and radius (in) of drill pipe or drill collar, respectively; Is the upward velocity (m/s) of mud in the annulus.
The shear rate of core end face is realized by adjusting the rotation speed of mud pump through frequency converter. Choosing a mud pump with reasonable displacement can simulate the displacement of mud pump at drilling site at will. During drilling, according to the hydraulic calculation results of mud annulus, only when the recommended rising speed of mud in the drill pipe or drill collar is 0.5 ~ 0.6m/s can a flat laminar flow be formed, thus meeting the requirements of drilling technology [4].
2.2 Calculation of core depletion rate
According to the dynamic filtration equation of drilling fluid, the dynamic filtration of drilling fluid or completion fluid through the core can be calculated by the following formula:
Oil and gas accumulation theory and exploration and development technology
Where: fd is the dynamic filtration rate (ml/cm 2 minutes); Δ θ is the dynamic filtration in Δ t time (ml); Δ t is the percolation time (s); A is the penetration area (cm2) of the end face of the core.
2.3 Calculation of permeability of core profile before and after dynamic pollution damage
Under the action of a certain pressure difference, fluid can flow through porous media. Generally speaking, its flow law can be described by Darcy's law. Therefore, the calculation of permeability parameters of each section of the core before and after dynamic pollution can be realized by applying Darcy's law formula. Because it is a multi-point test, the formula of Darcy's law can be written as:
3 implementation effect
The technical products of this project have been popularized in Jianghan, Jiangsu, Daqing, Dagang, Jilin, Zhongyuan, Southern Exploration Company, Karamay, Tarim and other oilfield units. A large number of experimental studies show that the application effect is good. It can measure the heterogeneity of core along the length direction, judge the permeability and damage depth of the same core before and after being damaged by drilling and completion fluid, and also evaluate the effects of various stimulation measures to optimize drilling and completion. The high-quality drilling and completion fluids screened by the "evaluation system" in the above oil fields have played a role in protecting oil and gas reservoirs, reducing production costs and increasing oil and gas well production, and achieved great economic and social benefits. The popularization and application of this achievement provides a brand-new evaluation means and method for reservoir protection technology research and oil and gas field evaluation, and also makes a major breakthrough in theory and experimental technology. The experimental research results will play a very important guiding role in the scientific decision-making of oil and gas field exploration and development scheme, the discovery of oil and gas fields, the improvement of oil and gas well production, the extension of oil field development cycle and the scientific research in the field of oil and gas reservoir protection.
The new evaluation methods and related technical products make scientific research achievements into productive forces in time, fill the gap in equipment manufacturing in related experimental technology fields in China, and have the international advanced level of similar technologies.
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