Bing Hou

Propagation area evaluation of hydraulic fracture networks in shale gas reservoirs

Abstract Based on hydraulic fracturing experiments in laboratory, the hydraulic fracture propagation in shale is analyzed, a method for evaluating the fracture propagation extent is proposed, and the effects of geological factors and engineering factors on fracture propagation are studied. “Stimulated Rock Area (SRA)” is proposed as an evaluation index for the hydraulic fracturing results. By analyzing the experiment results, it is found that hydraulic fracturing in shale reservoirs can generate a complex fracture network; a lower stress difference in brittle shale formation and a shorter distance between hydraulic fracture and bedding plane lead to a larger SRA and more complex fracture geometry; a fracture network is more likely to generate in the case that the angle between horizontal maximum stress direction and bedding plane is 90° or large enough, or the approaching angle between hydraulic fracture and well-opened natural fracture is close to 90°; a higher brittle mineral content leads to better fracturing ability; low fluid viscosity and high flow rate lead to a large SRA; a variable flow rate increases the possibility that the hydraulic fracture communicates with bedding planes and natural fractures.

The Treatment of Refinery Heavy Oil Sludge

During the process of crude oil refining, large amounts of oily sludge, which contains oil, benzenes, phenols, and other odorous and toxic substances, can be produced in refineries. All of these substances are legally classified as hazardous waste. However, oily sludge is rich hydrocarbons with high potential energy and the average calorific value is above 3,900 kcal/kg. Based on the characteristics of oily sludge in refineries, a new type of oily sludge treating agent has been developed that converts the oily sludge into fuel. This agent can achieve the rapid gel breaking and dehydration of oily sludge. Without adhesion and agglomeration, the dehydrated sludge with higher calorific value is easy to be dried and burned. The experimental results indicate that the burning ash and exhaust gas produced from the combustion can meet the requirements of environmental emissions standards in China after the oily sludge treated by fuels-based technology. This process has expanded a new technical method for the harmless disposal and utilization of oily sludge.

A Wellbore Stability Model for a Deviated Well in a Transversely Isotropic Formation Considering Poroelastic Effects

To analyse wellbore stability phenomena when drilling through a transversely isotropic formation such as shale, a wellbore stability model is developed based on the coordinate transformation method and complex variable elasticity theory. In order to comprehensively consider the anisotropies in the transversely isotropic formation, the model includes the followings: 1. thexa0elastic anisotropy due to the sedimentation effect and naturally developed fractures and 2. thexa0strength anisotropy due to the poor cementation between bedding planes and natural fractures. The model is further generalized by accounting for an arbitrary wellbore trajectory under an arbitrary in situ stress orientation. Next, the model is used in a parametric study that includes factors such as elastic anisotropy, strength anisotropy, multiple weak planes, in situ stress anisotropy, and poroelastic anisotropy, all of which can have a great influence on wellbore stability. Finally, a correction for a frequently used failure criterion has been made to ensure that the newly developed model is comprehensive and accurate for wellbore stability analyses in highly heterogeneous formations.

Experimental Investigation About Influence of Pre-existing Fracture on Hydraulic Fracture Propagation Under Tri-axial Stresses

To evaluate the complexity of fracture network, a series of hydraulic fracturing tests were conducted to investigate the influence of a pre-existing fracture on hydraulic fracture propagation under tri-axial stresses. The pre-existing fracture was prepared with different dip and strike angles. Experimental results demonstrated two basic types of phenomena, i.e., crossing or no-crossing a pre-existing fracture. They can be clearly identified from the relationships among strike angle, dip angle and in situ stresses. Two empirical relationships were proposed to describe the interactions between the pre-existing and hydraulic fractures. These relationships can be useful to predict the hydraulic fracture propagation in a naturally fractured reservoir, although its accurate determination requires the more experimental and theoretical studies.

Experimental investigation on fracture initiation and non-planar propagation of hydraulic fractures in coal seams

Abstract True tri-axial test system was deployed for fracturing simulation of coal outcrops to investigate the initiation and propagation of hydraulic fractures in vertical and directional wells. The influences of in-situ stress and cleats on non-planar propagation of hydraulic fractures in directional wells under different relative azimuths were analyzed. The test results show that the general propagation pattern of hydraulic fractures is jointly controlled by azimuth, cleats and in-situ stress. As the relative azimuth increases, the hydraulic fractures become more complicated in geometry and subject to increasing pumping pressure and propagation pressure. If the hydraulic fractures are initiated along a direction skewed with wellbore, the effect of cleats would alter the extension path and appear distortion of hydraulic fractures, inducing more complicated fracture geometry near the wellbore, with many fractures at the initiation point. Compared with vertical wells where I-shaped or X-shaped hydraulic fractures are formed, directional wells often have twisty propagation of dominant fractures near the wellbore and presence of multi-level fractures, which impede the further extension of hydraulic fractures in coal seams.

Analysis of Non-Planar Multi-Fracture Propagation from Layered-Formation Inclined-Well Hydraulic Fracturing

Current research shows that layered formation barriers can have a significant impact on the extension of fracture height; however, there are few studies on inclined-well near-wellbore fracture propagation shapes and penetrating patterns near the interface. We performed a true triaxial hydraulic fracturing experiment to study the layered formation of inclined-well near-wellbore and interface fracture propagation geometries influenced by formation conditions and perforation schemes. The results revealed that horizontal stress differences, perforation phase angles, borehole azimuths, and interlayer minimum horizontal in situ stress differences were the main factors that controlled the fracture propagation geometry. Under the conditions of large differences in horizontal stress, large perforation phase angles, and large angles between the borehole azimuth and the maximum horizontal in situ stress azimuth, the near-wellbore cracks presented a single main fracture with a large number of secondary fractures; in addition, the main and secondary fractures changed orientations. With moderate horizontal stress differences and less severe angle parameters, the fracture propagation geometry was simplified, forming a single main fracture. When all three parameters were small, the cracks displayed multiple main or network fractures. The surface morphology of spatial distribution was complex and the seam surface was rough. Under a crossing condition, the pattern of the penetrating fractures was highly affected by the near-wellbore fractures when the interlayer minimum horizontal in situ stress differences were small. Under large interlayer minimum horizontal in situ stress differences, the interface fractures began to deflect and generate new branches. The fluctuation and increase in fracturing pressure was caused by the dispersion of the fracturing fluid flow from multi-fractures and the large number of seam surfaces.

Drilling fluid loss model and loss dynamic behavior in fractured formations

Abstract In view of the lost circulation in fractured formations, a two-dimensional transient model for describing a power-law drilling fluid loss in an arbitrarily-oriented, compressible, permeable, rough-walled fracture was introduced. In this model, the mechanical fracture aperture and fracture tortuosity were considered to investigate the effect of fracture roughness on fluid loss dynamics. The governing equation of power-law fluid loss model was given and solved to analyze the fluid loss dynamics in fractured formations. The results show that the shear thinning behavior of power-law drilling fluid can result in high fluid loss rate at the initial stage of loss event; the fluid loss rate decreases as the fracture tortuosity increases, meanwhile, the effect of fracture tortuosity on fluid loss rate will decrease as the fracture aperture becomes larger; the larger the initial fracture aperture, fracture dip, fracture dimensions or fracture length, the higher the fluid loss rate will be; the fluid loss rate of rectangular fractures is much lower than that of square fractures; the higher the total leak-off coefficient, the higher the fluid loss rate will be; the fluid loss rate is the highest when the wellbore intersects the fracture at the center location; the fluid loss rate increases sharply as the differential pressure increases; the larger the normal stiffness of the fracture, the lower the mud loss rate will be.

Identification of leak zone pre-drilling based on fuzzy control

The key factor of plugging operation is how to identify leak zone as well as the difficult point for drilling operation in complex formation. Drilling fluids leakage and reservoir contamination frequently occurred due to the traditional method of identification of leak zone that lost circulation had already happened before detected. In this paper, the difficult problem of technology in identification of leak zone before drilling is solved by using fuzzy control theory. According to analyzing relevant parameters of lost circulation, the relationship between Euclid approach degree and lost circulation is established by using fuzzy relationship of lost circulation parameters. The field application indicated that this method is more accurate and workable in forecasting and practicing whereas the cost is effective. Above all, good results have been achieved in predicting the risk of leak zone by introducing this method.

Dynamic Compressive Behavior of Concrete at High Temperatures

For investigating the effect of temperature on the dynamic properties of concrete material, tests for cylindrical concrete specimens at 23°C ~ 800°C were carried out by using Split Hopkinson Pressure Bar (SHPB) apparatus, and the strain rates ranged from 30/s to 220/s. Effects of temperature and strain-rate on the dynamic behavior of concrete were analyzed. The results show that: above 4000C, the dynamic compressive strength of concrete decreases with increasing temperature, and the enhancements of strain-rates on the compressive strength of concrete depend significantly on temperatures. Moreover, both strain-rate and temperature can enhance the peak strain of concrete.

The Damage and Deformation Mechanism of Soft Mudstone in Drilling Engineer

Under pressure and activity difference between drilling mud and poro fluid, the degredation of mudstone mechanic features will change with the saturation time. It reveals that the reduction of the mudstone strength parameter and the decrease of the elastic modulus are the results of hydration stress development after the mudstone hydration. This paper proposed that the damage of soft mudstone is caused by the hydration stress development. After introduced the internal damage variable in the linear constitutive equations of viscoelastic materials, the approximate equation about the changing rate of the internal damage variables and the changing rate of the hydration stress can be got.