Huihu Liu

Response characteristics and mechanisms of dynamic fluid field for well interference of coal bed methane group wells in production block

According to production data and reservoir data of 16 coal bed methane (CBM) wells in southern Qinshui Basin, this paper draws the contour map of groundwater fluid potential at 8 moments in the production monitoring area and establishes three-dimensional visualization model of superimposed pressure drop funnel in CBM well with Matlab mathematical software; discusses the response relationship between well interference and dynamic fluid field on the basis of analyzing dynamic change features of groundwater fluid potential and evolution features of superimposed pressure drop funnel and puts forward an evaluation program of dynamic fluid field for well interference. The research result shows that dynamic fluid field has a good response relationship with well interference of CBM well and is manifested by the corresponding relation between evolutionary phase and space distribution. Evolution features of dynamic fluid field can be used to judge the phase and degree of well interference. The stage when well interference does not form is corresponding to the failure stage of original groundwater fluid potential and evolutionary phase of single-well pressure drop funnel. CBM wells do not have well interference and pressure drop funnel exists in the form of independent funnel. The space distribution of groundwater fluid potential is balanced. Due to the influence of groundwater fluid potential distribution, formation water flows to the shaft from the scope of pressure drop funnel. The stage when well interference forms preliminarily is corresponding to the stage of differentiation and reconstruction of groundwater fluid potential and formation stage of local superimposed pressure drop funnel. CBM wells start to have well interference and the degree of superposition of pressure drop funnel increases in local areas. “Low-lying” collecting area of groundwater fluid potential forms in superimposed area. Coal bed water flows to this area. The stabilization stage of well interference is corresponding to the formation and stabilization stage of new groundwater fluid potential and formation stage of regional superimposed pressure drop funnel. Regional superimposed pressure drop funnel is basically mature. New groundwater fluid potential centering on superimposed pressure drop funnel basically forms and coal bed water flows to the center of well network from surrounding areas.

Triple medium physical model of post fracturing high-rank coal reservoir in southern Qinshui Basin

In this paper, influences on the reservoir permeability, the reservoir architecture and the fluid flow pattern caused by hydraulic fracturing are analyzed. Based on the structure and production fluid flow model of post fracturing high-rank coal reservoir, Warren-Root Model is improved. A new physical model that is more suitable for post fracturing high-rank coal reservoir is established. The results show that the width, the flow conductivity and the permeability of hydraulic fractures are much larger than natural fractures in coal bed reservoir. Hydraulic fracture changes the flow pattern of gas and flow channel to wellbore, thus should be treated as an independent medium. Warrant-Root Model has some limitations and can’t give a comprehensive interpretation of seepage mechanism in post fracturing high-rank coal reservoir. Modified Warrant-Root Model simplifies coal bed reservoir to an ideal system with hydraulic fracture, orthogonal macroscopic fracture and cuboid matrix. Hydraulic fracture is double wing, vertical and symmetric to wellbore. Coal bed reservoir is divided into cuboids by hydraulic fracture and further by macroscopic fractures. Flow behaviors in coal bed reservoir are simplified to three step flows of gas and two step flows of water. The swap mode of methane between coal matrix and macroscopic fractures is pseudo steady fluid channeling. The flow behaviors of methane to wellbore no longer follow Darcy’s Law and are mainly affected by inertia force. The flow pattern of water follows Darcy’s Law. The new physical model is more suitable for post fracturing high-rank coal reservoir.

Simulation Experiment of the Anaerobic Degradation Law of Municipal Solid Waste

Using four sets of self-designed devices, the simulation experiment was carried out, which lasted 11 months. By monitoring the content of volatile solid, fats, crude fiber and humic acid, the anaerobic degradation law of the organic fraction of municipal solid waste (OFMSW) was studied. The results show that: (1) OFMSW degradation amount takes up 82.3% of the total at the acidification stage, so the acidification stage is the main period of OFMSW degradation. (2) Methanation inhibits the degradation of fats strongly, and the fats degradation rate decreases from 4.4 g-kg -1 -d -1 to 0.4 g-kg -1 -d -1 rapidly at the methanation stage. (3) There is great difference among the degradation degree of hemicellulose, cellulose and lignin, and their degradation rates are 66.9%, 51.6% and 7.3% respectively. Hemicellulose/lignin and cellulose/lignin decrease linearly with degradation time, which can be used as a stabilization evaluation index in the process of OFMSW degradation. (4) LFG disturbance action and pH increase are two possible reasons to lead the total extractable hymatomelanic acid and humus acid decrease rapidly along with LFG production increase.