A Coupled Model for Predicting Flowing Temperature and Pressure Distribution in Drilling Ultra-Short Radius Radial Wells

In the production process of high-temperature and high-pressure gas wells, it is very important to understand the changes of the temperature and pressure parameters in the wellbore with the depth of the well. Based on the conservation of fluid energy, momentum, and mass in the wellbore, considering the influence of high-temperature and high-pressure gas wells on the temperature and pressure of the wellbore under the coupling of fluid velocity, density, and Joule–Thomson effect, a wellbore temperature and pressure prediction model was established based on this. Then, we could obtain wellbore temperature and pressure distribution along the well depth. The comparison with the actual wellbore data of Tarim X gas well and XX well in Southwest China shows that the calculation result of the multifactor coupling model is less than 3% of the field measured data, which verifies the accuracy of the multifactor coupling model result. Based on this, the effects of different gas production and production time on the temperature and pressure of high-temperature and high-pressure gas well boreholes were analyzed. The results show that for the Tarim X gas well, when the gas production is 80 × 104, 90 × 104 and 100 × 104 m3/day, the corresponding wellhead temperatures are 56.1, 65.3, and 69.8 °C; the corresponding wellhead pressures are 62.4, 62.2, and 62.0 MPa. When the production time is 1 day, 10 days, and 20 days, the corresponding wellhead temperatures are 61.5, 63.6, and 64.8 °C, respectively; the corresponding wellhead pressures are 63, 62.8, and 62.4 MPa.

Influences of formation water invasion on the wellbore temperature and pressure in supercritical CO 2 drilling

Calculation of the wellbore temperature and pressure distribution during supercritical CO2 fracturing flowback process

Supercritical carbon dioxide (SC-CO2) drilling technology is a new type of drilling technology, which has developed rapidly since the end of the last century. With lower jet erosion threshold pressure, higher jet erosion speed, and excellent hole cleaning capabilities, the SC-CO2 drilling receives much attention. However, for SC-CO2 fluid, the density, viscosity, heat capacity, Joule-Thomson coefficient, and so on are more sensitive to changes of wellbore temperature and pressure, and at the same time the change of parameters will react to the wellbore temperature and pressure, so they should be widely investigated while drilling with SC-CO2. The wellbore temperature and pressure coupled flow model was developed for SC-CO2 drilling, and then the wellbore pressure, temperature, and density profile were analyzed in an example. The results showed that the calculation results have a larger difference between this model and the reference model; the main reason is that the viscosity, isobaric heat capacity, thermal conductivity of SC-CO2, etc. were deemed as a fixed value in the reference model, and the wellbore temperature and pressure were not coupled while calculating.

Numerical simulation of the abrasive supercritical carbon dioxide jet: The flow field and the influencing factors

The low temperature condition of permafrost in Arctic region affects the rheology of drilling fluids and the distribution of temperature and pressure in the wellbore during drilling. In order to understand the influence law of permafrost in Arctic region on the temperature and pressure distribution in wellbore and provide a basis for the design and construction for drilling in Arctic region, a model to predict the wellbore temperature and pressure of drilling in Arctic region was built. It was based on the analysis of the influence of low temperatures on the rheology of water-based and oil-based drilling fluids, considering the coupling between permafrost and wellbore. By comparing the measured and test results, it was verified that the prediction accuracy of the proposed model met the requirements of drilling in Arctic region. The model was used to simulate the temperature and pressure distribution in a wellbore in Arctic region under the conditions of no circulation or pump function. The results showed that the drilling fluids absorbed the heat of the high-temperature formation and returned to the annulus transferring the heat to the permafrost in shallow part of the wellbore during the circulation. This process thawed the permafrost near the wellbore and the wellbore temperature was lowered due to the heat consumed by thawing. The circulating friction in annulus increases with the increase of circulation time. The longer the pump shutdown lasts, the closer the temperature of drilling fluid to the formation temperature in the wellbore. The larger the annular circulation pressure loss, and the higher the pump pressure. The research results can provide a basis and guidance for design and construction of drilling in Arctic region.

ABSTRACTA new numerical calculation model for wellbore temperature and pressure for SC-CO2 jet fracturing was proposed in this research. In our model, the impact of tubing, casing, and cement on heat transfer, and the heat generated by fluid friction losses are all taken into consideration. The CO2 physical properties are calculated by the Span–Wagner and Vesovic models. Based on our calculation model, the factors that may affect the wellbore temperature and pressure are discussed. The results indicated that ignoring the influence of the cement sheath thermal resistance on heat transfer would lead to a wellbore temperature higher than the actual value. The wellbore CO2 pressure is always higher than its critical value, but the CO2 temperature at the jet point in some cases is lower than its critical value. The wellbore CO2 temperature is increased with the increase in injection temperature and cement sheath thermal conductivity and the decrease in annulus injection rate and coiled tubing injection rate. However, the decrease in the coiled tubing injection rate and increase in the cement sheath thermal conductivity are the only effective ways to ensure that the CO2 temperature at the jet point exceeds its critical value.

Investigation on rock-breaking characteristics of hard sandstone by non-planar PDC cutters under high confining pressure

Experiment on rock breaking with supercritical carbon dioxide jet

Supercritical carbon dioxide (SC-CO2) 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-CO2, it is prospective for swirling-round SC-CO2 jet to improve rock erosion efficiency further. Rock damage mechanisms of swirling-round SC-CO2 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-CO2 jet are divided into two aspects. On the one hand, swirling-round SC-CO2 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-CO2, and existing fractures are expanded, which led to fractures joining together and massive rocks split off.

The supercritical carbon dioxide (SC-CO2) jet offers many advantages over water jets in the field of oil and gas exploration and development. To take better advantage of the SC-CO2 jet, effects of nozzle configuration on rock erosion characteristics were experimentally investigated with respect to the erosion volume. A convergent nozzle and two Laval nozzles, as well as artificial cores were employed in the experiments. It was found that the Laval nozzle can enhance rock erosion ability, which largely depends on the pressure and temperature conditions. The enhancement increases with rising inlet pressure. Compared with the convergent nozzle, the Laval-1 nozzle maximally enhances the erosion volume by 10%, 21.2% and 30.3% at inlet pressures of 30, 40 and 50 MPa, respectively; while the Laval-2 nozzle maximally increases the erosion volume by 32.5%, 49.2% and 60%. Moreover, the enhancement decreases with increasing ambient pressure under constant inlet pressure or constant pressure drop. The growth of fluid temperature above the critical value can increase the enhancement. In addition, the jet from the Laval-2 nozzle with a smooth inner profile always has a greater erosion ability than that from the Laval-1 nozzle.

The initiation and propagation behavior of fractures induced by supercritical carbon dioxide (SC-CO2) jet fracturing is significant to evaluate stimulated reservoir volume (SRV). However, the propagation characteristics of fractures induced by SC-CO2 jet in layered rocks with layers having different mechanical properties have not yet been studied. In this study, four groups of artificial sandstones were used to conduct SC-CO2 jet fracturing experiments and investigate the fracture initiation and propagation behavior in hard and soft layered rocks. A strain collection device was employed to monitor the strain changes of the specimens during the experiments, and after the experiments, a three-dimensional scanner was used to obtain the morphologies of the main fractures. Experimental results showed that the SC-CO2 jet fracturing can be divided into the pressurization of the perforation pressure stage and fracture propagation stage, and the fractures initiation and propagation is intermittent. Three types of main fractures have been found—longitudinal fracture, transverse fracture and oblique fracture—and the formation mechanism of the main fractures has been elaborated. The rock strength can affect the number and complexity of fractures created and the fracturing rate, and the Young’s modulus of rock has an effect on fracture propagation length. The fractures mainly develop near the perforation and are difficult to propagate to another layer with different mechanical properties. The result in our study is conducive to the application of SC-CO2 jet fracturing technology in the field.

Supercritical carbon dioxide (SC-CO2) jet is capable of decreasing the threshold pressure of rock breakage and mitigating formation damage, owing to its low viscosity, high diffusivity, and extremely-low surface tension. The swirling-round jet holds the advantages of both a swirling jet and a round jet. Therefore, the comprehensive technique, swirling-round SC-CO2 (SR-SC-CO2) jet, is expected to substantially enhance rock-breaking efficiency. However, theoretical analysis of the flow field characteristics of SR-SC-CO2 has not been reported yet. This work aims to lay a theoretical foundation for employing SR-SC-CO2 in drilling and fracturing. The flow field is simulated using Naiver-Stokes equations and the RNG k-ε turbulence model. Sensitivity analysis, regarding pressure drop of the nozzle, confining pressure, fluid temperature, jetting distance, the diameter of the nozzle’s central hole, and grooving area, are performed. We show that the combined swirling-round SC-CO2 jet flow could maintain a relatively larger axial as well as tangential velocity compared to a single approach of swirling jet or round jet, enabling one to acquire a deeper oillet and expand the perforation area effectively. The simulation results substantiate the enormous potential of SR-SC-CO2 in improving rock-breaking efficiency and clarify the influence of relevant parameters on the impact pressure of the jet flow.

For the sake of solving the problem that it is difficult to dynamically monitor the wellbore temperature and pressure of hydrocarbon gas injection well and accurately predicting the bottom hole injection pressure, a mathematical model to describe wellbore temperature and pressure distribution is presented according to the heat transfer principle, the energy conservation law and the momentum theorem. The Shiu-Beggs wellbore temperature calculation method is used in this model to avoid errors caused by inaccurate thermodynamic parameters, and the pressure gradient equation is modified by introducing correction coefficients to improve the calculation precision of the model in practice. The fourth-order Runge-Kutta method was used to solve the model, and the new model was analyzed and verified by actual field data. The results show that the wellbore temperature is nonlinearly distributed, while the wellbore pressure is linearly distributed, and the bottom hole pressure calculated by this model is more accurate than that calculated by other methods. This study can play a certain guiding role for the injection scheme design of hydrocarbon gas injection well.

At present the concept of instantaneous equilibrium is often adopted for simulating the wellbore pressure and temperature distribution in heavy oil wells. In this paper, the mathematical model was built and the diffusion of gas in the oil phase was researched. It proves that the non-equilibrium phenomenon is not obvious in convenient oil wells and it could be overlooked, while in heavy oil wells the non-equilibrium phenomenon is too prominent to be overlooked. Basing on the mass conservation principle, the momentum conservation principle and the energy conservation principle, the calculated model for wellbore pressure and temperature in heavy oil wells considering of the non-equilibrium effect was established. One example shows that the model can accurately reflect the flowing laws in heavy oil wells, which has a relative value for engineering.