Methanol has been used to prevent hydrate formation in industrial handling of hydrate forming mixtures containing water for many decades. Ethanol is also used for the same purpose in countries that have easy access to low price ethanol, like for instance Brasil. Common to these small alcohols is that they also have surfactant properties that will promote hydrate formation, but when added to water in sufficient amounts, the hydrate prevention characteristics will dominate. These alcohols will primarily prevent heterogeneous hydrate formation on the interface between water and a separate hydrate phase. The effect of “alcohol” on both of these routes to hydrate formation are investigated and compared to experimental data. In particular we also investigate the effects of these small alcohols on Gibbs free energy for the hydrate formed on the new, shifted, stability conditions. Gibbs free energy is generally higher than hydrate formed from pure water. Enthalpies of hydrate formation are also higher for hydrate formed from water containing alcohols. These are negative numbers, so in absolute values released formation enthalpy is lower. The presence of these alcohols in water will also prevent homogeneous hydrate formation from dissolved hydrate formers in water. Glycols have more important roles in other routes to hydrate nucleation. Heterogeneous hydrate nucleation towards mineral surfaces is feasible in different ways. Polar hydrate formers like H₂S and CO₂ can adsorb directly on rust, and as discussed here, are able to form hydrate from adsorbed state on rust surface. Non-polar hydrocarbons like, for instance methane might get trapped in structured water and then nucleate to hydrate. Some research on this is published and further research is in progress. Glycols have very strong attraction to rust and corresponding chemical potentials for adsorbed glycols on rust are favourable enough to facilitate phase transition from glycols dissolved in water over to adsorption. Injection of glycol in gas processing plants has been used by industry for many years and in many cases it might even be economically and technically feasible compared to expensive drying units. Exceptions are situations that will lead to water/glycol freezing. But even in multiphase transport of hydrocarbons with various water cuts, mixtures of alcohols might be a technically efficient solution in which the small alcohols may be very efficient as discussed above and glycols may go through adsorption phase transition from water solution over to glycol film on rust and prevent hydrate nucleation towards rust surface. This possible strategy requires more theoretical work as well as experimental investigation. On the basis of thermodynamic analysis and calculations of hydrate formation from different routes, it is argued that real natural and industrial systems are unable to reach thermodynamic equilibrium. It is therefore a need for a consistent thermodynamic platform with a uniform reference system for all phases. We propose and demonstrate a residual thermodynamic model system for all phases.

A breakthrough has been recently made in the hydrocarbon exploration of the Permian pyroclastic rocks in the Jianyang Area, western Sichuan Basin, China. With an aim to decipher the impacts of the eruption environment, the temperature of hydrothermal fluids, and the paleo-salinity on the formation of authigenic mineral assemblage and pores, this study implements comprehensive petrographic and geochemical studies through the integrated core and thin section analyses. The data presented demonstrate that the Permian volcanic intervals are intensively affected by an event of Emei taphrogeny. During basaltic magma upward migration, fractional crystallization of anorthose results in slightly-alkaline magma. The specific pyroclastic rocks are formed by the eruption of slightly-alkaline magma in the sea or a salt lake and subsequent hydrothermal alteration. During deposition and diagenesis, the authigenic mineral association is constrained jointly by the sodium-rich and high salinity water environment, and mid-high temperature, high-salinity hydrothermal fluid. Specifically, the sodium-rich hydrothermal fluid, which may sustain till the late diagenesis stage, caused pervasive albitization of pyroclastic rocks, then leading to mineral transformation and formation of a series of mineral associations. Therefore, zeolitization of volcanic glass and vesicle-infillings of zeolite is an essential condition for later mineral transformation and dissolution. Albitization of analcite, recrystallization induced by deep hydrothermal fluids, and both meteoric and deep burial dissolution expanding the micro-pore space ultimately formed porous pyroclastic reservoirs.

In order to study the propagation laws of acoustic wave of coal samples from the Upper Permian Xuanwei Formation in the east of Yunnan Province, China, under saturated water and dry conditions, the basic physical parameters, acoustic parameters and anisotropic parameters were obtained through the experiments. Based on FFT and wavelet analysis theory, the spectral characteristics of coal samples under different conditions were studied. The results show that physical parameters of coal samples in different directions have different values, that is, the anisotropy of coal samples is obvious. When the coal samples are saturated with water, the acoustic velocities and the attenuation coefficient increase, whereas the dominant frequency decreases. The signal amplitude of the frequency domain significantly decreases, that is, the internal structure of coal samples is damaged. The P-wave velocity and S-wave velocity increase with the increase of the confining pressure, whereas the anisotropy parameters decrease with the increase of the confining pressure. Overall, this study provides the basis to understand basic acoustic information and anisotropy characteristics of coal samples.

Filtration control is important to ensure safe and high efficient drilling. The aim of the current research is to explore the feasibility of using basil seed powders (BSPs) to reduce filtration loss in water-based drilling fluid. The effect of BSP concentration, thermal aging temperature, inorganic salts (NaCl and CaCl₂) on the filtration properties of bentonite/basil suspensions was investigated. The filtration control mechanism of BSP was probed via water absorbency test, zeta potential measurement, particle size distribution measurement, and filter cake morphologies observation by scanning electron microscope. The incorporation of BSPs into the bentonite suspension generated acceptable rheology below 1.0 w/v%. The BSPs exhibited effective filtration control after thermal aging at 120°C, but less efficiency at 150°C. After thermal aging at 120°C, the bentonite suspension containing 1.0 w/v% BSPs could resist NaCl and CaCl₂ pollution of 5.0 w/v% and 0.3 w/v% respectively. Besides general filtration control behaviors, the exceptional water retaining capability formed by numerous nanoscale 3D networks in the basil seed gum and considerable insoluble small particles in BSPs might further contribute to the filtration control. The excellent filtration properties bring basil seed a suitable and green candidate for the establishment of high-performance drilling fluids.

In the last decade, there has been an increasing interest in understanding the effects of changing injected water salinity on the performance of oil reservoirs. This paper aims to investigate the effects of injected water salinity on oil recovery of an Egyptian oil reservoir (Bahariya formation). An experimental work program has been performed using 25 core plugs and 5 different water salinities to study the effects of changing water salinity during both secondary and tertiary stages of waterflooding. The objectives of the experimental work were to (1) investigate the effects of the low water salinity on oil recovery and (2) identify the optimum water salinity and the main reservoir parameters for application of low salinity waterflooding project (LSWF) in Bahariya formation.

The results revealed that there is an optimum salinity for waterflooding in the secondary flooding stage. However, for the tertiary flooding stage, the results showed that the controlling factor is not decreasing the salinity, but rather changing the salinity (e.g. either increasing or decreasing). It was also clear that applying the optimum salinity in the secondary recovery stage is more effective than applying it in the tertiary recovery stage. Furthermore, the results showed that the positive impact of LSWF may be expected in reservoirs with high amount of kaolinite, high values of CEC, and low amounts of plagioclase feldspar.

This study is an original contribution to develop guidelines for designing optimum salinity waterflooding projects in sandstone reservoirs.

The contribution of geomechanics to provide a rigorous quantification of porosity changes and associated permeability changes is often neglected when considering hydrocarbon production. However, it often has significant effects on production rates and ultimate recovery. For the cold heavy oil production with sand (CHOPS) technique, geomechanics is the key for reservoir simulations and promoting successful operations. In fact, the technique employed in CHOPS significantly affects the stress state within the reservoir by inducing “on-purpose” formation damage. It is not only vital to comprehend the behaviour of the reservoir during production, but it is crucial to identify how to harness that behaviour to improve productivity. In order to simulate the mechanical behaviour of unconsolidated sand material, an elastoplastic damage model was formulated. Fluid-flow-geomechanical modelling was then performed for predicting individual well behaviour and overall field performance. The combined effect of fluid-flow and geomechanics improved predictions with respect to oil, water, and gas production rates at key wells. Fluid rates matched satisfactorily most of the wells. In addition, the onset and propagation of equivalent wormhole networks were quantified throughout the production history. This enabled quantification of the volume of produced sand at individual wells. The comparisons between the measured and simulated sand volume rate at well locations showed reasonable agreement. Such calibrated models can then be used for the placement of new wells to optimize production.

In view of the classical Lucas-Washburn equation, which can only describe the spontaneous imbibition of single wetted capillary, a tilted composite capillary model with circular cross section, composed of different wettability capillary wall was established. The model can describe the spontaneous oil-water imbibition of water-wet capillary, oil-wet capillary and mixed wetting capillary. Through numerical solution of the model equation, it is found that the component content of the capillary walls, the capillary radius and the oil-water viscosity ratio have great effects on the spontaneous oil-water imbibition. Effects of capillary inclination angle and inertia force on spontaneous oil-water imbibition are related to the capillary scale. Effects of capillary inclination angle and inertia force can be ignored in small radius capillary, while effects of inclination angle and inertia force can not be ignored in large radius capillary.

In this paper, a new 3D visualization technical method was developed for hydraulic fractures using micro-seismic monitoring. This technical method consists of four steps: i. interpret the geologic hydraulic fracture model based on seismic source location data from micro-seismic monitoring; ii. develop a hydraulic fracture indication model, relying on the 3D spatial freeze-frame of micro-seismic monitoring sources from hydraulic fracturing; iii. construct a hydraulic fracture density model using the intensity from the micro-seismic monitoring; and iv. implement a 3D visualization of the hydraulic fractures, relying on the spatial constraints of the density model, the hydraulic fracture indication model, and the properties of the hydraulic fractures. This proposed technical method was used to produce 3D visualizations of the hydraulic fractures in well X in the Jiao reservoir, China, and the 3D visualizations of the distribution, development, extent and cutting relationships of hydraulic fractures were successfully realized. The results show that this technical method can be used as a practical and reliable approach to characterize hydraulic fractures.

The challenges found in geothermal well drilling have forced the industry to develop new significant cost effective, time saver technologies to go for deeper geothermal resources beyond their traditional limits. To overcome these challenges, the new Dual String Drilling (DSD) technology which is based on penetration pathway of drilling fluid and rock cuttings during drilling a well. The principle of DSD employs drilling fluid flows through the annulus of inner and outer string pipe while cutting from the bottom of the well through inner pipe. The paper describes the novel Dual String Drilling (DSD) technology, predicting their occurrence and advantages on drilling of geothermal well. The outcome shows that with DSD approach a lot of time will be saved to circulate the kick out of the well. Additionally, the characteristic response of DSD enables to improve the hole cleaning capacity, to prevent pipe stuck, better well stability, reduction in torque and drag, to remove the dynamic equivalent circulating density gradient in geothermal wells. Moreover, the paper also depicts the system and method for dual coil tubing drilling of horizontal well which follows the same principle as DSD. The comparison of DSD with conventional drilling assesses that the DSD technology is affordable and appropriate for geothermal well drilling.

In this study, the effects of wax deposition on submarine multiphase pipelines are investigated. In order to understand the mechanism of wax deposition in submarine multiphase pipelines, a wax deposition model in a submarine pipeline was established using the OLGA wax deposition module, and key factors influencing this phenomenon were analyzed. Additionally, a multifactor impact analysis of wax deposition was performed via the orthogonal test method. The results indicated the relative influence of five factors on oil-gas-water three-phase wax deposition, namely, oil flow rate, water content, inlet temperature, gas-oil ratio, and outlet pressure. Then, the main influencing factors of wax deposition in a multiphase pipeline flow were extracted, and the wax deposition prediction model was established. The wax deposition rate under different operating conditions was simulated using the OLGA wax deposition simulation module. The SPSS software was used to perform nonlinear regression analysis under different working conditions. In this manner, the constant terms in the wax deposition prediction model for a submarine multiphase pipeline were obtained. The prediction model could be used to programmatically predict wax deposition along a multiphase pipeline by programming the initial waxing conditions. By using this method, the wax deposition prediction model of an M − N submarine multiphase pipeline was obtained under different working conditions. After comparing the predicted and the OLGA simulation results, it was concluded that the established wax deposition model can be used to accurately calculate the wax deposition in a submarine multiphase pipeline within an allowable error range. If the physical properties and operating parameters of the conveying medium in a multiphase pipeline are given, the developed oil-gas-water three-phase wax deposition model can be used to predict the distribution of wax deposition in submarine multiphase pipelines without laboratory experiments. The results of this study can help production units understand the waxing situation of pipelines in time in order to scientifically formulate a pigging plan and avoid pipeline blockages and shutdowns.

The irregular wellbore trajectory caused by the wellbore deviation and fluctuation makes a significant effect on the torque and drag in extending and direction drilling, especially for wellbore trajectory with obvious deviation in the drilling direction. As a consequence, a new quasi-three-dimensional wellbore tortuosity evaluation method is developed. The new method incorporates the effect of fluctuation frequency and amplitude of oscillating wellbore trajectory; a weight coefficient index that quantifies the effect of tortuosity of one segment trajectory to the entire trajectory; a ‘Peak-Valley’ principle that can decompose the irregular wellbore trajectory in various scale lengths. The studies show that the deflection angle between the segments of tortuous wellbore increases the torque and drag by strengthening the contact behaviors between the drillstring and borehole. Therefore, the deflection angle is introduced to quantify the effect of deviation in the drilling direction on wellbore tortuosity. The evaluation results of two field cases demonstrate the new method which is adapted to the wellbore trajectory fluctuating with various characteristics and can reflect the actual state of wellbore tortuosity with severe oscillation more effectively and accurately.

Aiming at the main problems in the design and analysis of well wall strengthening for fractured formations, a three-dimensional (3D) numerical simulation scheme is proposed. The three-dimensional finite element software is used to analyze the mechanical behavior of fractures and the pressure sealing process, and evaluate the stress cage effect. The main features of the model are as follows: (1) The equivalent fractures in the analytical model represent the function sum of the mechanical behavior of all fractures on the well wall, which is a functionally equivalent crack.(2) When evaluating the stress cage effect, the shape of the crack wedge filled with the plugging agent particles is formed by simulating the fractures opening process under the injection pressure, not a given regular shape.(3) In the model of calculating bull heading of block agent, the liquid pressure on the well wall is the injection pressure, which is a variation increased with time. The fluid pressure on the well wall in the stress cage calculation model is generated by the initial pore pressure. (4) The numerical evaluation of the stress cage effect is achieved by calculating the increase amplitude FX of the minimum hoop stress on the well wall. Using this model, several sets of injection pressure design values can be used for pressure plugging numerical simulation and stress cage effect evaluation calculation, and then the optimal and accurate quantitative value of “injection pressure, block agent particle size, safe mud window upper bound” are found through comparison. Finally, through an engineering example of horizontal well drilling pressure sealing in a shale gas reservoir developed by a fracture, we use the above theoretical tools to introduce the process and results of the numerical analysis of the extended mud window drilled in the shale gas fissure reservoir.