Tian Shouceng

Research on Two-Phase Closed Thermosyphon to Improve Fluid Temperature Distribution in Wellbores

Abstract A two-phase closed thermosyphon (TPCT) is introduced to improve fluid temperature distribution in wellbores by utilizing its characteristics of efficient heat transfer. Laboratory experiments show that TPCT in wellbores can heat the upper fluid in wellbores by absorbing the surplus energy of the lower fluid in the wellbore, and no extra energy is consumed. The roles of TPCT are affected by several factors. The type of working media needs to match with the inlet temperature of simulation oil. A filling ratio of 15% is optimal for different TPCT wellbores in experiments. With higher vacuum degree in the TPCT cavity, TPCT has a better role. With higher simulation oil flow rate, the role of TPCT is worse.

Transmission Characteristics of DPSK Mud Pressure Signals in a Straight Well

Abstract Transmission characteristics of differential phase shift keying (DPSK) pressure signals transmitted in a downhole mud channel are researched by theoretical and numerical methods. With the control logic analysis of a rotating valve in continuous-wave telemetry, a DPSK pressure signal mathematical model is built in accordance with principles of communications and mathematical analysis. In the condition of water-based drilling fluids, drill pipes of a straight well are divided into a number of sections in accordance with wellbore pressure distribution. By transfer function analysis of all the sections, a numerical expression of the signal along the entire length of the vertical drill pipes is obtained and the influence of transmission distance, internal diameter of drill pipes, carrier frequency, drilling fluids viscosity, and air voids on the signal amplitude are analyzed. Numerical calculation shows that the influence of drilling fluids viscosity and air voids on the DPSK signal are the most notable for the signal transmission.

Key issues and investigation of horizontalwell drilling and multistage fracturing in shale gas reservoir

Unconventional shale gas is rapidly increasing as an available source of natural gas in the worldwild. Horizontal well drilling and multistage fracturing are two principle techniques of shale gas resources production. Benefiting most from these two techniques, the United States, Canada, and China have become only three countries to produce shale gas in commercial quantities. The key technical issues emerged in the horizontal drilling and fracturing involve the rock fragmentation issues, wellbore trajectory optimization and control, wellbore stability, cementing and its quality control for long horizontal lateral, and hydraulic fracturing design. Although some progress associated with those technical issues have been achieved in China, there are still many geologic and engineering challenges: (1) the low rate of penetration and fast bit wearing for both PDC and Cone bits are still the primary issues, which makes hard achieve the “one-trip” drilling; (2) wellbore collapse and lost circulation are serious with a certain collapsing period due to natural fractures system; (3) complex multi-fractures propagation behaviors still need to be understood and the fundamentals of fracturing design should be established after undstanding multi-fractures propagation behaviors.

Mechanisms of rock breaking by swirling-round SC-CO 2 jet

Supercritical carbon dioxide (SC-CO 2 ) jet is characterized by low rock breaking threshold pressure and high rock breaking rate. Swirling-round jet, taking the advantages of both swirling and round jet, enjoys high rock breaking efficiency. By integrating swirling-round jet and SC-CO 2 , it is prospective for swirling-round SC-CO 2 jet to improve rock erosion efficiency further. Rock damage mechanisms of swirling-round SC-CO 2 jet are investigated by means of rock-erosion experiments and scanning electron microscope (SEM) observation. The selected core samples include shale, dolomite as well as sandstone. For shale, no macro-deformation occurs and microscopic damage is discovered, forming tiny cracks. For dominate and sandstone, erosion holes form, and crystal particle cleavage as well as inter-particle rupture occur. According to the observation results, the rock damage mechanisms of swirling-round SC-CO 2 jet are divided into two aspects. On the one hand, swirling-round SC-CO 2 jet breaks rock by combining axial impinging, radical tension and circumferential shear. On the other hand, with characteristics of low viscosity, compressibility and strong diffusivity, numerous micro fractures are caused by SC-CO 2 , and existing fractures are expanded, which led to fractures joining together and massive rocks split off.

Shale rock fragmentation behaviors and their mechanics by high pressure waterjet impinging

High pressure waterjet technology is a potentially advanced technology to improve the drilling efficiency of shale rock formation. The success of waterjet drilling requires more insight into the rock fragmentation behaviors and their mechanics. In the present study, a series of submerged waterjet impinging trials were carried out on the outcrop shale rock collected from the Longmaxi Formation, Sichuan Basin, China. Simultaneously, the sandstone was selected as the candidate of the control group. The macro fragmentation behaviors and their micro structures were acquired by the scanning electron microscope (SEM) and computed tomography (CT) techniques. The rock mechanics and mineral composition before and after experiments were measured by the standard ISRM method and X-ray diffraction, respectively. Particularly, the grain size distributions of cuttings were obtained by a laser particle size analyzer. Results show that the efficiency of shale waterjet drilling is ultralow, which the rate of penetration and the ultimate drilling depth cannot reach the half of those sandstone. SEM imaging shows that shale is ultra-tight in which the illite clay weaves into a network and the dolomite embeds into the network. It just likes a concrete material resulting in the high compression strength. Since the static pressure of waterjet is lower than the compression strength, the common compression-shear failure does not happen, but only the tensile fracture occurs and makes the rock spallation for the initial crushing. With the penetration depth increasing, the waterjet impinging force is not able to make the rock tensile or shear failure. Only the particle erosion becomes a dominant failure mechanism for shale rock where the mineral particles are removed or crushed from rock matrix as fine cuttings. This work provides the theoretical guide for improving the shale rock drilling efficiency by water jetting.

Flaw Location of Pipeline based on the Accelerometer

Abstract The pipeline is the most economic and effective means to transport large quantities of oil and natural gas over long distances. However, in the long term, pipeline flaws may appear because of erosion, abrasion, unexpected damage and so on, which would weaken the pipeline safety performance and even result in leakage and pipe explosion accidents. For timely discovery of flaws and establishing optimal strategy of maintaining the pipeline, the in-served pipeline will be periodically online evaluated by using the smart PIG (pipeline inspection device) to detect flaws and locate them in the body of the pipeline. A method for flaw location of the pipeline is presented in this article, where a high resolution servo accelerometer CX-3 is used to measure the axial acceleration of the smart PIG in a pipeline to acquire the precise distance walked by the smart PIG by integral operation of the acceleration value to time variable and error correction. Basing on the linear relation between the distance and time label a flaw location precision about 0.2% can be reached by indoor experimental measurement. This experimental result shows that the location precision based on the accelerometer is higher than the Odometer wheels now in use and the technology will satisfy the pipeline inspection need by further research and development.

Results of Bench-Scale Oil Displacement of Novel Polymer Solution in Daqing Oilfield

Abstract In order to improve the dissatisfied oil displacement results of conventional low molecular weight polymers in some thin and poor reservoirs of the Daqing Oilfield in China, two new polymers with low molecular weight are introduced. A series of laboratory experiments were performed to evaluate the performance index and oil displacement results of the novel polymers. The results show that the new polymers have the characteristics of higher viscosity, better salt and shearing resistance, and better solubility than conventional polymers, and the viscoelasticity and shearing resistance of the new polymers increases with a decrease in molecular weight. Bench-scale oil displacement experiments indicate that the oil displacement results of the new polymers are better than those of the conventional polymers with the same molecular weight and the performance will be better with a decrease in molecular weight. Novel polymers have a favorable matching relationship with low-permeability reservoirs that are fit for wide application in thin and poor reservoirs.