|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Liu, Qingyou (Chengdu University of Technology / Southwest Petroleum University) | Zhao, Jianguo (Chengdu University of Technology) | Zhu, Haiyan (Chengdu University of Technology) | Dong, Run (Southwest Petroleum University, Chengdu)
ABSTRACT: Hydraulic fracturing of hot and dry rock (HDR) usually produces a single main fracture. However, a single main crack is prone to produce "thermal short-circuit effect" in the heat transfer process, thus reducing the heat transfer efficiency. This will lead to the early abandonment of the HDR wells and restrict the development of the HDR resources. In view of the technical problems faced by the development of HDR resources, the idea of using downhole robots to implement blasting-hydraulic fracturing is put forward. The novel exploitation technology of the HDR resources can avoid the single main fracture caused by the in-situ stress, rock strength and natural fracture, and form a complex fracture network as far as possible, which can improve the thermal interaction area of the HDR and avoiding the "thermal short-circuit effect". Based on the novel exploitation technology of the HDR resources, the working mechanism of the downhole robot is studied. A prototype of the downhole robot and a special experimental bench and system are developed. On this basis, a series of the ground experiments such as static/dynamic experiments and control reliability of the downhole robot have been completed. Finally, the new exploitation technology of the HDR resources is of great scientific significance and engineering application prospects for the economic and efficient development of HDR resources.
Meng, Mianmo (China University of Petroleum-Beijing) | Ge, Hongkui (China University of Petroleum-Beijing) | Shen, Yinghao (China University of Petroleum-Beijing) | Li, Qinyu (China University of Petroleum-Beijing) | Yu, Jiayao (China University of Petroleum-Beijing)
ABSTRACT: Hydraulic fracturing plays an important role in developing tight sand gas. Large amount of fracturing liquid was injected into the formation to produce fracture. The flowback rate usually is very low. The retention liquid can cause serious aqueous phase trapping (APT). Some tight reservoir can auto-remove its APT after well shut-in for a period of time. The nuclear magnetic resonance (NMR) associated with imbibition was carried out to research the mechanism of APT auto-removal in tight reservoir. From Taiyuan Formation NMR experiment, liquid preferentially filled into small pores, and then gradually filled into the medium pores. In H8 Formation, liquid fills into both small pores and medium pores uniformly. No preferential displacement appears. After flow-back, liquid is prone to move from medium pore to small pores in Taiyuan Formation because small pores have strong imbibition force; liquid has less capacity to move from medium pores to small pores in H8 Formation because all pores have equal imbibition force. Therefore, the aqueous phase trapping (APT) is less serious in Taiyuan Formation than H8 Formation. Our research is conducive to learning the mechanism of APT auto-removal in tight gas reservoir.
ABSTRACT: Hydraulic fracturing creating an artificial fractures or establishing a fracture network is an effective technology to conduct fluids in multiwell enhanced geothermal system (EGS). Rock mechanics tests show that deep hot-dry rock (HDR) always has high strength and in-situ stress, the traditional hydraulic fracturing concept of form bi-wing artificial fractures will face enormous challenges in deep HDR. Mini-fracturing test and main-fracturing reveal that the tensile failure not only leads to an ultra-high pumping pressure, but also limits the stimulation radius. Natural fracture is one of the most important parameters controlling the rock failure mode, increasing the injectivity index and reducing the injection pressure. Hybrid tensile failure is the most likely failure mode for deep HDR hydraulic fracturing, which includes the shearing and propagating of nature fractures and increases the conductivity and radius of the fracture network. The elasto-plastic constitutive model reveals the recoverable elastic strain and irreversible plastic strain mechanism, and characterizes the mechanical aperture change of rough surface of nature fractures. The effective conductivity aperture of natural fractures affected by combined effect of heat transfer, fracture fluid flow, shearing dilation and chemical dissolution. Therefore, the challenge and future development of hydraulic fracturing in deep dry-hot rock in EGS is the coupling of Thermal-Hydro-Mechanical-Chemical (THMC).
Chen, Zhaowei (CNPC Engineering Technology R&D Company Limited) | Huang, Rui (CNPC Engineering Technology R&D Company Limited) | Zhou, Xiaojin (PetroChina Southwest Oil & Gas Field Company) | Song, Yi (PetroChina Southwest Oil & Gas Field Company) | Qing, Chun (PetroChina Southwest Oil & Gas Field Company) | Yang, Yang (Sichuan Changning Natural Gas Development Co., Ltd.)
ABSTRACT: In Changning and Weiyuan shale gas blocks, casing deformation occurred in more than 30% of wells during hydraulic fracturing, which restricted the efficient development of shale gas in China. Ning 201-H1 was atypical well which experienced casing deformation. The characteristics of casing deformation, include deformation time, deformation position and deformation shape, were analyzed, and the results indicate that the casing deformation was caused by a small fault slip. Using Microseismic monitoring data and ant tracking data, the dip and inclination angles of small faults were identified, and the mechanical activity of the fault was analyzed based on the in-situ stress and treating pressure data. The results show that under the in-situ stress conditions and treating pressure, the fault is critically stressed and was activated during fracturing, which caused casing deformation. The characteristics of cementing quality data, fracturing curve and microseismic data were analyzed. Due to poor cementing quality, the fracturing fluid may break through the gap between casing and formation during fracturing, intrude the fault and finally activate the fault. Therefore, in order to avoid casing deformation, it is recommended to improve cementing quality and avoid small faults.
Liu, Y. (Southwest Petroleum University, Chengdu) | Chen, P. (Southwest Petroleum University, Chengdu) | Ma, T. S. (Southwest Petroleum University, Chengdu) | Wu, B. S. (Tsinghua University, Beijing) | Zhang, X. (CSIRO Energy) | Wu, B. L. (CSIRO Energy)
ABSTRACT: Wellbore strengthening (WBS) treatments have been widely applied to improve formation bearing capacity and to mitigate lost circulation during drilling fractured formations with narrow mud weight window. However, the mechanisms of WBS are still not completely understood since the fluid-solid coupling process between plugging zone and drilling fluid is previously simplified. In this paper, a fully coupled numerical model that includes rock elastic deformation, fluid flow and plugging mechanics is employed to study the evolution of near-wellbore stress and fracture opening and internal pressure before and after WBS. The numerical result is in good agreement with the published ones, verifying the accuracy of the present model. The numerical results indicate that the hoop stress can be enhanced in compression after plugging the fractures. The evolution of fracture opening and internal pressure in fracture suggest that WBS treatment can prolong the time to reach the fracture growth state. The existence of the plug can also significantly change the normal stress distribution. In addition, the impact of plug permeability on its shear failure pattern is analyzed, and the relations of plug failure time and wellbore strengthening index (WSI) with wellbore pressure are discussed in detail.
ABSTRACT: The present geothermal gradient values of the Dongpu Depression range from 20.0 to 56.5 °C/km, with an average value of 34.8 °C/km. Its terrestrial heat flow varies from 37.8 to 106.8 mW/m2, with an average value of 66.8 mW/m2. The Dongpu Depression could be characterized as a medium-temperature field between stable and active tectonic areas. The high heat flow value in the Dongpu Depression is closely associated with the Changyuan, Huanghe and Lanliao basement faults and thin lithosphere thickness. There are abundant geothermal resources in the Dongpu Depression. Low-temperature to medium-temperature sandstone-hosted hydrothermal systems are evaluated to exist in the intervals less than 3500 m. The Cenozoic bottom temperature is more than 150 °C except the western gentle slope zone. The Ordovician carbonate strata are deeply buried, generally more than 4000 m. Therefore, most of the high temperature carbonate-hosted hydrothermal system are predicted to develop in the intervals below 4000 m based on the measured temperature and modeling.
ABSTRACT: Thermal devices such as thermosyphons and heat pipes have a wide variety of applications from underground heat exchangers and temperature control to de-icing of civil engineering infrastructure to aerospace electronic devices. Understanding and optimization of their operating conditions is thus important. In this paper, a weighted decision matrix was used to determine what working fluid is the most appropriate for use in a closed two-phase thermosyphon and an artery wick heat pipe. The fluid is required to have a high merit number, compatibility with all materials that might be found in a heat pipe, high maximum permissible heat flux, and a broad operating temperature range. The primary objective of this study is to develop models to define optimum working fluids to be used for a given device design. The model for thermosyphons estimates the maximum heat flux using the flooding limit, boiling limit and dry-out limit; the model for a heat pipe uses the boiling limit, capillary limit, entrainment limit, sonic limit and viscous limit. The maximum heat flux is then determined by taking the minimum of the heat transfer limitations and dividing it by the radial area of the condenser section for each operating condition. This value was then used as a criterion for a weighted decision matrix, along with the merit number, the number of compatible pipe materials, and operating temperature range. The model was applied to low-temperature range working fluids such as water, ammonia, and heptane and allows evaluation of what fluid is optimal at any particular device geometry as well as operational conditions such as temperature and pressure.
Gou, Bo (Southwest Petroleum University, Chengdu) | Zeng, Mingyong (Southwest Petroleum University, Chengdu) | Guo, Jianchun (Southwest Petroleum University, Chengdu) | Lai, Jie (Southwest Petroleum University, Chengdu) | Liu, Zhuang (Southwest Petroleum University, Chengdu) | Ma, Huiyun (Petro China Southwest Oil & Gasfield Company) | Zhou, Changlin (Petro China Southwest Oil & Gasfield Company) | Liu, Fei (Petro China Southwest Oil & Gasfield Company)
ABSTRACT: The acid-rock reaction on fracture wall has effect on the mechanical properties of rock, which would further affect the acid-fracture propagation and strength of the pillars. The effects of hydrochloric acid on the elastic and mechanical properties of tight dolomite have been assessed under triaxial stress in the laboratory. Tight dolomite were divided into acid-treatment and un-treatment groups. During the acid-treatment process, samples were exposed to hydrochloric acid in the reaction kettle with different acid-rock reaction time under high temperature and high pressure. All samples were subjected to triaxial loading up to mechanical failure under the same condition. The results show that with increase of acid-rock reaction time, acid only causes dissolution on the contact face and deepens etching groove, while the porosity and permeability of samples barely change after acid-treatment. After acid-treatment, the failure form of rock is converted from elasticity to elasticity-plasticity, and the plasticity failure becomes obvious gradually with increase of acid-contact time. The elastic moduli and Poisson's ratio reduce significantly after acid-treatment; however there is no obvious relationship between the reduction range of mechanical parameters and acid-contact time. This study reflects the effect of acid on the mechanical of tight dolomite under high temperature high pressure.
Shentu, Junjie (China University of Petroleum, Beijing) | Lin, Botao (China University of Petroleum, Beijing) | Dong, Jingnan (CNPC Engineering Technology R&D Company Limited) | Yu, Huiyong (PetrolChina Xinjiang Oilfield Company, Engineering Technology Research Institute) | Shi, Shanzhi (PetrolChina Xinjiang Oilfield Company, Engineering Technology Research Institute) | Ma, Junxiu (PetrolChina Xinjiang Oilfield Company, Engineering Technology Research Institute)