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Provided that the hydraulic boundary conditions at the wellbore wall are identified as permeable (PBC) and impermeable (IMPBC) and that the assumption of plane strain holds, the present paper formulates a newly porothermoelastic analytical solution, which is based on the thermodynamic principles, in Laplace space domain for inclined borehole. The adopted linear porothermoelastic model embodies the transient heat transfer process in the presence of local thermal non-equilibrium (LTNE) during the derivation. The solution is available for the cases where the wellbore axis of inclined wellbore is perpendicular to the isotropic plane of the low permeable transversely isotropic porous medium under non-hydrostatic stress field condition. The wellbore problem is decomposed into axisymmetric and deviatoric loading cases. The numerical results of the time-dependent distributions of field variables are obtained by virtue of performing the inversion technique for Laplace transforms. An integrated geomechanical wellbore stability model is proposed, which is not only comprised by the abovementioned new porothermoelastic solution, but also associated with the theoretical derivations of strength criteria to evaluate the rock to shear failure, which include Mogi-Coulomb criterion and single weak plane criterion. When a horizontal borehole is drilled along the direction of in the minimum horizontal in-situ stress, the numerical comparative analyses in the present paper examine the combined influence of material anisotropy and thermal effect, which embody in the LTNE and local thermal equilibrium (LTE) models, on the thermally induced pore pressure, stresses and the shear and tensile failure regions around the wellbore.

Given that the hydraulic boundary conditions at the wellbore wall are identified as permeable (PBC) and impermeable (IMPBC) and that the assumption of plane strain holds, the present paper formulates an analytical solution, which is based on fully coupled linear porothermoelastic model with the thermal osmosis and thermal filtration effects, in Laplace space domain. The solution is available for the cases that the wellbore axis of inclined wellbore is perpendicular to the isotropic plane of the transversely isotropic medium under non-hydrostatic stress condition. The wellbore problem is decomposed into axisymmetric and deviatoric loading cases. The numerical results of the time-dependent distributions of field variables are obtained by virtue of performing the inversion technique for Laplace transforms. The sensitivity analyses are performed on the key parameters to thermal osmosis and thermal filtration effects. The effect of thermal filtration on temperature is also illustrated. The numerical comparative analyses in the present paper examine the influence of material anisotropy of poromechanical parameters and thermal properties, which embody in porothermoelastic-osmosis-filtration model and common porothermoelastic one, on the thermally induced pore pressure and stresses. Finally, an integrated geomechanical wellbore stability model is developed to investigate the compressive and tensile failure extents of horizontal wells. The model is involved with three aspects, i.e. the coordinates transformations pertaining to wellbore and weak plane systems, the criteria to evaluate the shear failure (including intact rock and weak plane) as well as tensile fracture, and the fully coupled porothermoelastic analytical solution. The developed porothermoelsatic analytical solution can provide a theoretical basis for multiple of aspects including the inversion of in-situ stress, geothermal reservoir stimulation and petroleum drilling design.

Piedmont tectonic belts are rich of oil and gas resources, however the intense tectonic stress and broken formation may cause great drilling problems in piedmont structures such as borehole collapse, lost circulation and gas cutting. Through analysis of in situ stress properties, bedding structure and mechanical characteristics, wellbore instability mechanism was expounded from rock mechanics, chemistry of drilling fluid and drilling technology. The high tectonic stress, formation strength decreasing and fluid pressure rising after mud filtrate seepage are main reasons for borehole collapse. The methods of calculating collapse and fracture pressure and determining drilling safety density window were put forward based on mechanical analysis. In order to reduce drilling problems in piedmont structures, some countermeasures should be taken from optimizing well track and casing program, using proper mud density, improving inhibitive and sealing ability of drilling fluid. Good sealing ability can reduce seepage and cut off pressure transmission, enhancing the effective support force. This is the key technology of maintaining wellbore stability in hard brittle shale in piedmont structures.

Research on the flow low in the slot of the slotted screen used in the unconsolidated sand formation is conducted with computational fluid dynamics method. Research on the erosion and corrosion of the slotted screen is presented with the calculation of flow field and the introduction of erosion model established by the Erosion and Corrosion Research Center of Tula. Moreover, the slot erosion characters and the maximum erosion with different production pressure difference and sand content are given. The result shows that: (1) the maximum value of the flow rate and the erosion appears at the horn mouth of the slotted screen; If the production pressure difference is enlarged, the amount of sand that flows into the inner of the screen will increase and the flow rate of the sand will increase sharply, which worsens the erosion of the screen; (2) the degree of the erosion of the slotted screen grows exponentially with the increase of the production pressure difference and initially increases and then decreases with the increasing of the sand content; the degree of the erosion reaches the peak value when the sand content is ten percent; and (3) the main erosion region is the middle part of the slot, and this region widens with the increasing of production pressure difference. The lower part of the screen is more damaged than the upper part.

Shale gas reservoirs are characterized by tight matrix, well-developed micro-fissures, and laminations. The study about the failure of shale under compression is of great significance to safe drilling operation and the subsequent reservoir stimulation. The variation of rock mechanical properties with the angle between the axial stress and bedding plane normal (coring angle) is analyzed based on laboratory tests. A failure criterion is applied and verified to describe the strength of shale. Moreover, ultrasonic technology is used to study the damage characteristics of shale during the uniaxial compression process. The experimental results show that shale strength decreases initially and then increases with the increase of the coring angle. The Young’s modulus and Poisson’s ratio increase with the increase of coring angle. In a compression process, damage is essentially the development of new micro-cracks induced by the compression. Shale failure is the microscopical reflection of the process of the generation and expansion of axial micro-cracks, so it is the result of damage accumulation. The variation of the lateral p wave velocity can function as a monitor of the development process of shale damage. The damage factor will increase in the linear elastic stage and then enlarge rapidly after entering the stage of unstable micro-crack expansion.

In recent years, Extended reach well (ERW) drilling technology is widely used in the offshore oil & gas fields in order to reduce the number of the drilling platforms. As it has notable characteristics such as the high deviation angle, large horizontal displacement and long open borehole interval the borehole stability increases the drilling risk and cost dramatically. To research the ERW borehole stability, including mechanical model, shale hydration test and the effect of circulating pressure loss in this paper, rock mechanics theory and hydraulics principle were comprehensively applied . The results show that, the safer drilling azimuth of the ERW in normal fault lies in the minimum horizontal principle stress direction; hydration radius increases with the passage of time, and the hydration collapsed rock has important influence on cutting beds and circulating pressure loss in annulus; the upper limit value of safety mud density decreases with the well depth increases, and when it deceases to the equivalent mud density of collapse pressure, the limit depth of the ERW is obtained. The research results provide relevant guidance on the ERW drilling, which can be used to determine the upper and lower safety mud weight limits, the best well trajectory selections and the well structure design.

Wellbore collapse is one of the often encountered problems when drilling through shale formations. The instability mechanism and effect factors should be made sure to adopt suitable countermeasures. The bedding shale's permeability was measured by experiment, and with this foundation, the effects of drilling fluid seepage on formation strength and wellbore stability were discussed. Results showed that laminar shale's permeability is anisotropic and random. The permeability is extremely low in the direction perpendicular to the bedding plane, and it is very high parallel to the bedding plane when there are interlayer microcracks. The drilling fluid permeating along the bedding plane leads to great decrease on cohesion and internal friction angle, and then decreases the shale formation's strength, finally leading to borehole shrinkage, pipe sticking, and borehole collapse. Increasing mud weight only is good for borehole stability in short term. However, it intensifies seepage finally and can't control boreh...

Sand production in deepwater gas fields can cause great harm, so it is vital to determine a reasonable production system. At present the prediction models of critical pressure difference of sand production in oil-gas wells are numerous, but among them there is no prediction model that aims at deepwater gas fields that the mining environment of high risks. The authors carried out a lot of experiments with real rock cores to simulate sand production in gas wells by using a set of self-developed radial displacement experimental devices. During experimenting they measured critical flow rates and critical pressure differences when sand production happened, and calculated the critical pressure differences of sand production under the condition of actual reservoirs. Comparing the results of the experiments with that of multiple sanding prediction models, the most suitable model for gas reservoirs was determined. Through doing error analysis and coefficient modification on the model, a simple and effective method...

At present, many oilfields were placed in the middle and late development period and the reservoir pressure depleted usually, resulting in more serious differential pressure sticking and drilling mud leakage both in the reservoir and cap rock. In view of this situation, a systematic prediction method of safety mud density in depleted oilfields was established. The influence of reservoir depletion on stress and strength in reservoir and cap formation were both studied and taken into the prediction of safety mud density. The research showed that the risk of differential pressure sticking and drilling mud leakage in reservoir and cap formation were both increased and they were the main prevention object in depleted oilfields drilling. The research results were used to guide the practice drilling work, the whole progress gone smoothly.

In order to reduce the oil and gas drilling risk and cost, the calculating method of collapse pressure was established to prevent borehole collapse in fractured shale formation. The method was coupled with borehole concentrated stress, induced stress by crack opened and pore pressure change. The influence law of borehole trajectory and crack occurrence was researched. The results show that, collapse pressure increases substantially in small dip fractured shale formation when the well deviation angle exceeds the critical value, and the increase speed is fastest in the direction of maximum horizontal principle stress; collapse pressure is lower when crack is nearly vertical and the tendency parallel to wellbore azimuth for the horizontal well, but when crack dip exceeds 30° and the tendency is not parallel to wellbore azimuth, it is more dangerous for drilling due to the higher collapse pressure. The research results can be used to solve wellbore instability problems and improve drilling efficiency in the similar regions.

This paper describes the method used in the depleted reservoir for analyzing horizontal in-situ stresses in order to define a stable mud weight window to maximize the efficiency of drilling process. The method combines wellbore sta- bility modeling, in-situ stress prediction, and pore pressure depletion during production process. In the presence of any hydraulically isolated fault blocks or other permeability barriers, the pore pressure depletion will cause horizontal stress changes in both magnitude and orientation. Furthermore, the changes of horizontal stress affect the wellbore stability of inclined wells. The results indicate that the reservoir depletion has notable effect on the safe mud weight window, espe- cially the fracture pressure. The fracture pressure may be overestimated in previous model, and the most stable well azi- muth is not static but varies over the lifetime of the oilfield. The research conclusions can provide significant reference for the mud weight design of directional well in depleted reservoir.

When the well with high-pressure packing sand control becomes invalid a relatively thick sand-gravel mixing zone will exist outside the casing. The mixing zone can hardly be cleared up in the process of later repeating sand control, so with the multiplicity of sand control increasing, the thickness of the mixing zone increases accordingly, which will do harm to the productivity of well. Aiming at this problem, the authors first analyzed the packing zone outside casing and then three optional solutions were given: fracturing packing sand control, casing external gravel packing zone acid pickling, and high-pressure variable diameter gravel packing technique. Especially, the authors proposed the technique of acid pickling of casing external gravel packing zone, and its technical ideas and main points were expounded for the first time; according to the Saucier method and the arch bridge theory, the authors analyzed the optimization of gravel size in the technique of high pressure variable diameter gravel pack...

Through the determination of mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field and the creep experiments on these rocks, the authors analyze the impacts of mineralogical compositions, deviatoric stress, temperature, and confining pressure on creep behavior and proposes the constitutive equation of steady-state creep rate by combining with the creep curve and rock parameters obtained by the experiments. The experiment results indicate that the main mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field are sodium chloride and calcium sulfate, where the content of sodium chloride can be up to more than 93%; the inherent mineralogical compositions are the internal factors that impact the creep characteristics of rock, along with the content of sodium chloride increasing, the rates of transient creep and steady-state creep increase accordingly; and as the deviatoric stress and temperature increase, the steady-state creep rate increase...

Deepwater shallow sediment is less-consolidated, with a rock mechanical behavior similar to saturated soil. It is prone to borehole shrinkage and downhole leakage. Assume the deepwater shallow sediments are homogeneous, isotropic, and ideally elastoplastic materials, and formation around the borehole is divided into elastic and plastic zone. The theories of small deformation and large deformation are, respectively, adopted in the elastic and plastic zone. In the plastic zone, Mohr–Coulomb strength criterion is selected. The stress and deformation distributions in these two zones, and the radius of plastic zone are derived. The collapse pressure calculation formula of deepwater shallow sediments under the control of different shrinkage rates is obtained. With the introduction of excess pore pressure theory in soil mechanics, the distribution rule of excess pore pressure in these two zones is obtained. Combined with hydraulic fracturing theory, the fracture mechanism of shallow sediments is analyzed and the theoretical formula of fracture pressure is given. The calculation results are quite close to the practically measured results. So the reliability of the theory is confirmed.

A macrocyclic thrombin inhibitor, cyclotheonamide B ( 1 , R=Ac) was synthesized via a new approach: guanidination of the ornithine-containing macrocyclic peptide ( 2 ). In comparison of various coupling reagents, pentafluorophenyl diphenylphosphinate (FDPP) gave the macrocyclic peptide ( 2 ) in good yield, and the configuration of the amino acid residue has been revealed to be important for the macrolactamization.