The analytical model of hydraulic fracture initiation for perforated borehole in fractured formation

Lei

Huang³

et al. 2021

Geofluids

Self Cite

Hydraulic fracturing is a necessary technique for shale gas exploitation. In order to have efficient stimulation treatment, a complex fracture network has to be developed, whereas with rich bedding planes and natural fractures, the mechanism of forming a fracture network is not fully understood and it is so tricky to predict propagation and initiation of hydraulic fracture. Therefore, in this paper, considering the strong anisotropy of shale reservoir, numerical simulation has been conducted to analyze fracture propagation and initiation on the basis of finite element and damage mechanics. Simulation results indicate that hydraulic fracture is not merely controlled by in situ stress due to strong anisotropy in shale. With plenty of bedding planes, hydraulic fracture tends to have initiation and propagation along the bedding plane. In particular, this influence becomes stronger with low strength and high development density of bedding planes. Additionally, in combination with natural fracture and bedding plane, the initiation point is usually on a natural fracture plane, causing relatively small breakdown pressure. In the process of fracture propagation, hydraulic fracture connects with natural fractures and bedding planes, forming dendritic bifurcation and more complicated paths. Numerical simulation proves that bedding plane and natural fracture are vital factors of hydraulic fracture. Compared to natural fracture, the bedding plane has a stronger impact on hydraulic fracture propagation. For the initiation of hydraulic fracture, natural fracture is the major effecting factor. The outcome of this study is able to offer theoretical guidance for hydraulic fracturing in shale.

Section: The Influence Of Development Density Of Bedding Plane On Hydraulicmentioning

confidence: 99%

The Investigation on Initiation and Propagation of Hydraulic Fractures in Shale Reservoir

Lei

Huang³

et al. 2021

Geofluids

Self Cite

“…1 Clay shale is a common geological formation, which is often encountered in drilling. Efficient drilling operation can make huge contribution to exploitation and development of oil and gas.…”

Section: Introductionmentioning

confidence: 99%

“…Efficient drilling operation can make huge contribution to exploitation and development of oil and gas. 1 Clay shale is a common geological formation, which is often encountered in drilling. Clay shale formation has high risk of wellbore collapsing, impairing drilling efficiency and causing huge economic losses.…”

Section: Introductionmentioning

confidence: 99%

Hydration index and hydrated constitutive model of clay shale using acoustic frequency spectrum

Energy Science & Engineering

Ding

Ranjith

et al. 2019

Self Cite

Clay shale is frequently encountered in drilling. With strong hydration capacity, when clay shale contacts with drilling fluid, rock structural and mechanical property will be affected, causing wellbore instability. Acoustic frequency spectrum is a significant parameter in geophysical logging. The influence of hydration on clay shale can be reflected in acoustic logging. Therefore, in order to identify hydration damage and have precise evaluation for hydration damage, a novel hydration damage index has been built on the basis of acoustic frequency spectrum. Meanwhile, considering the influence of hydration, hydrated constitutive model has been proposed using this new index. Results demonstrate that acoustic frequency spectrum has clear modification due to hydration damage. In the hydration evolutionary process, fracture initiation and propagation happen, decreasing acoustic amplitude and dominant frequency. The whole hydration evolutionary process exhibits S curve with clear three stages. In the initial stage, changing ranges of acoustic amplitude and frequency are small. In the middle stage, clear fracture propagation can be noticed and fracture network is formed, boosting the change of acoustic frequency spectrum. Finally, acoustic frequency spectrum becomes stable, meaning hydration damage has reached its limitation. Hydration damage degree is variable with different conditions, but the tendency still remains typical S curve. Stress‐strain curves simulated from hydrated constitutive model are in good agreement with results of uniaxial compressive test, indicating this model can be used to express shale mechanical property in hydration evolutionary process. Findings of this paper can offer theoretical reference for evaluating hydration damage and are advantageous for drilling operation in clay shale formation.

“…When it comes to fractured reservoir, single weak plane criterion and tensile criterion are frequently employed to calculate fracture initiation . According to these criteria, rock is composed of two parts, that is, rock matrix and fracture plane.…”

Section: Introductionmentioning

confidence: 99%

A novel analytical model of initial fracture pressure for horizontal staged fracturing in fractured reservoir

Liang

Ding

Energy Science & Engineering

et al. 2019

Self Cite

The horizontal well-staged fracturing technology has been widely used in many oilfields to enhance well production by creating fracture network. Accurate prediction of fracture initiation is significant for successful hydraulic fracturing operation. However, hydraulic fracture initiation in fractured reservoir is highly tricky due to its rich natural fractures and artificial fractures previously created during staged fracturing. These fractures are thought to be major factors in conducting efficient staged fracturing in fractured reservoir. Therefore, in this paper, induced stress from artificial fractures has been analyzed by using two-dimensional analytical model. Besides, based on the assumption that rock in the formation is composed by rock matrix and fracture plane, considering tensile and shear failure type, failure criterion with multiple natural fracture planes has been developed. By combining impacts from natural fractures and artificial fractures, we establish an analytical model to calculate initial fracture pressure for horizontal staged fracturing in fractured reservoir. These results demonstrate that induced stress is associated with artificial fractures' location, height, and number. This induced stress leads to increment of initial fracture pressure, restricting fracture initiation. Due to natural fractures, there are three types of initiation, which are tensile failure along rock matrix, tensile failure along natural fracture, and shear failure along natural fracture plane. When rock failure is related to natural fracture, initial fracture pressure decreases and is variable with natural fracture plane occurrence. Especially, with large number of natural fractures, only one initiation type exists, which is tensile failure along natural fracture. Additionally, for horizontal borehole, influencing extent of fracture planes is associated with wellbore trajectory. The case study proves the applicability of this analytical model, meaning it can be used to guide horizontal staged fracturing in oilfield. K E Y W O R D Sartificial fracture, fracture initiation, fractured reservoir, natural fractures, staged fracturing