(1) meets the requirements of simulating formation fluid flow between fractures in coal reservoir;
(2) Meet the requirements of simulating the distribution effect of fractures in coal reservoirs after reservoir reconstruction;
(3) Meet the requirements of simulating the occurrence state of coal reservoirs in coal-bearing strata;
(4) Meet the production mode requirements of simulating coalbed methane well drainage → depressurization → gas production.
Through a series of explorations and attempts, the main system structure of the physical simulation experimental instrument is determined, including computer monitoring system, sample preparation system, pumping replacement system, physical simulation system, pulverized coal storage system, pulverized coal analysis system, power system and so on.
(1) computer monitoring system: mainly composed of computer control platform and displacement diversion monitoring platform. The computer control platform provides semi-automatic and semi-manual functional services, and the control of the displacement diversion monitoring platform is realized by computer, which can meet the requirements of physical simulation experiments under different conditions. At the same time, the displacement diversion monitoring platform can realize the liquid displacement mode, automatically adjust the displacement speed and pressure, monitor the diversion situation in real time and record the discharged products in real time.
Table 5-3 Experimental Scheme for Studying the Influence of Coal Structure Difference on Pulverized Coal Output
(2) Sample preparation system: mainly composed of sample preparation mold, lifting pressure cylinder, platform support, etc. The preparation of samples requires auxiliary equipment, such as crusher, standard sample sieve and electronic balance. Firstly, the coal sample is crushed by a crusher and screened by a standard sample sieve to select coal particles with a certain particle size. According to the size and shape of the sample preparation mold, under the extrusion of the lifting pressure cylinder, the coal brick sample is made for the physical simulation experiment of pulverized coal production. The system needs to control the lifting of the pressure cylinder through the computer monitoring system to provide stable pressure for sample preparation.
(3) Pumping displacement system: mainly composed of advection pump, liquid storage container, displacement liquid, diversion chamber, seamless steel pipe, flange, etc. The working principle of the system is to provide a stable fluid with a certain flow rate by adjusting the pumping power of the advection pump. This fluid will inject the replacement fluid in the liquid storage container into the diversion chamber at the same rate to replace the coal bricks in the diversion chamber. At the same time, the left and right sides of the diversion chamber need to be provided with liquid inlet and outlet channels respectively, and pressure measuring channels and corresponding flanges should be installed at the liquid inlet and outlet ends. In this process, the displacement diversion monitoring platform is used to adjust the pumping power of the advection pump and set parameters such as displacement period and data recording frequency.
(4) Physical simulation system: it is mainly composed of coal brick samples, quartz sand, diversion chamber, metal gasket, plastic sealing ring, differential pressure sensor, lifting pressure cylinder, platform support, etc. The working principle of the system is to artificially create cracks by sandwiching quartz sand particles in two coal bricks, and simulate the fracture extension state of coal reservoir after reservoir reconstruction. The pumping displacement system provides a certain flow of displacement fluid to the flow chamber to simulate the flow process of formation fluid between fractures in coal reservoir; The computer monitoring system adjusts the lifting pressure cylinder to generate stable confining pressure on the coal bricks in the diversion chamber, and simulates the occurrence state of coal reservoirs in coal-bearing strata. The system is carried out with the cooperation of computer monitoring system, pumping displacement system and physical simulation system. Displacement fluid is provided by advection pump, extrusion force is provided by lifting pressure cylinder, displacement flow, cylinder pressure and other parameters are adjusted and recorded by displacement diversion monitoring platform, and coal bricks in diversion chamber are guaranteed to be sealed by metal gasket and plastic sealing ring.
(5) Coal powder storage system: mainly composed of electronic balance, seamless steel pipe, beaker, etc. The working principle of the system is to collect the liquid discharged from the physical simulation system and its pulverized coal, and at the same time, the discharged liquid is weighed in real time through the displacement and diversion monitoring platform and the data results are stored.
(6) Coal powder analysis system: mainly composed of laser particle size analyzer, filter paper, filter, constant temperature dryer, electronic balance, microscope, scanning electron microscope, X-ray diffractometer, etc. The working principle of the system is to test the particle size distribution of pulverized coal produced under different experimental conditions with a laser particle size analyzer. Filtering and drying the pulverized coal in the discharged liquid by using a filter and a constant temperature dryer; Accurately weighing the dried pulverized coal particles with an electronic balance; Microscope, scanning electron microscope and X-ray diffractometer were used to analyze the micro-morphology and material composition of pulverized coal. The output physical characteristics of pulverized coal are studied from the perspectives of particle size, quality, microstructure and material composition.
(7) Power system: mainly composed of distribution box and motor. The system provides power and power supply for other systems of physical simulation experimental equipment.
Fig. 5- 1 Schematic diagram of physical simulation experimental instrument for pulverized coal output
According to the functional requirements of the above-mentioned physical simulation experimental instrument, the experimental instrument is designed as shown in Figure 5- 1. On the basis of investigation and considering the feasibility of physical simulation experiment, HXDL-ⅱ acid corrosion fracture deflector is used as the testing instrument. The instrument can simulate formation pressure and temperature under standard experimental conditions, realize gas-liquid two-phase displacement process and evaluate fracture conductivity. The equipment flow is shown in Figure 5-2. According to the description of the above-mentioned physical simulation experimental device, the main system of the acid etching crack deflector selected can meet the requirements of the experiment, and the components of the device can meet the requirements of the experiment. The parameters of this instrument are set according to SY-SY-T 6302— 1997 "Recommended Method for Short-term Conductivity Evaluation of Fracturing Proppant Filling Layer".
Figure 5-2 Flowchart of Acid Corrosion Fracture Flowmeter