Gas Influx Research Articles

Determination of absorption mass transfer coefficients of methane into drilling fluid base oils at elevated pressures

Absorption mass transfer coefficients (kla) of methane into two widely used drilling fluids base oils-internal olefins and diesel were determined at elevated pressure. A laboratory-scale bubble column (0.0254 m diameter and 0.71 m static liquid height) was used to perform the experiments. Ranges of superficial gas velocity (0.0045–0.0491 m/s) and system pressure (0.69–2.07 MPa) were covered. Based on the results, the effects of the varying parameters on kla have been discussed. Based on the observations, an empirical model was developed for the volumetric mass transfer coefficient as a function of superficial gas velocity and density. This correlation fitted well (R2 > 0.98) with the measured kLa values for the investigated range of operating conditions. This study gives new quantitative insights into the absorption kinetics of methane into two drilling fluid base oils, which are important for improving gas influx management with non-aqueous drilling fluids.

Boundary Control and Estimation for Underbalanced Drilling With Uncertain Reservoir Parameters

In underbalanced drilling (UBD), the bottom hole pressure is kept below pore pressure, causing pressure-dependent influx of reservoir gas into the wellbore that makes the system unstable at low drawdowns. In this article, we propose a feedback controller which stabilizes the system, represented by the “reduced drift flux model (DFM),” around an arbitrary pressure setpoint, while using only topside measurement and assuming unknown reservoir parameters. A particular challenge with this problem is the distributed and highly nonlinear nature of the system dynamics, where the “reduced DFM” models gas–liquid flow as a nonlinear transport equation with a nonlocal integral source term. An observer estimates the distributed gas concentration, downhole pressure, and reservoir parameters by solving the system dynamics backward relative to how the gas rises in the well. The control inputs are then constructed by designing target states over the next sampling period and again solving reversed dynamics to obtain the required topside pressures. The resulting controller is implemented with a 2-min zero-order hold to accommodate the actuation limitation situation on an actual drilling rig. Finally, the results are illustrated in simulations with an industry standard drift flux formulation as the plant model.

Development of ECRH-based methods for assisted discharge burn-through: Experiment and simulation

Electron Cyclotron (EC) waves will be routinely used in future reactors not only for plasma heating and/or non-inductive current drive during the flat top but also to assist the plasma start-up phase in large tokamaks with superconductive coils. In ITER, for example, EC start-up is foreseen since first plasma operation. To limit the level of stray radiation, ECRH can be used after ohmic breakdown, as a robust solution to successfully sustain the plasma burn-through in the presence of pre-filling gas and impurity influx from the wall. On ASDEX Upgrade (AUG), a series of dedicated experiments have been performed using EC heating (X2) with a controlled Ne impurity injection in the prefill phase, to mimic non-favourable burn-through conditions such as would be expected in a discharge following a disruption event. The time for EC heating onset has been optimised to assist the early burn-through and a scan of the Ne concentration has been performed to find the threshold for successful burn-through conditions for two ECH power levels (0.7 and 1.4 MW). The toroidal magnetic field flexibility has been also documented, with the cold resonance position being shifted up to 13% in major radius to match the ITER condition. These experiments showed that optimised settings of ECH power (onset and duration of the pulse) have a key role in making feasible the early Ne burn-through (with Ne concentration up to 14% and EC power of 1.4 MW). Successful pulses will be extended to study stationarity and clean up properties. For an efficient and robust use of such a technique, it is essential to develop appropriate models capable of describing present experiments and of extrapolating (or predicting) to future scenarios. In this work, the predictive 0D model for the burn-though phase BKD0 [1] has been used to reproduce experimental results and estimate the power required for a successful burn-through as a function of the impurity concentration, finding that ECH power of 1.4 MW is required to sustain burn-through with more than 20% of Ne. The scalability of the model has been also tested on TCV [2] and its implication for ITER will be discussed.

Atmospheric pressure discharge sustained by millimeter radiation in a waveguide plasmatron

In the developed waveguide plasmatron with combined gas influx, a nonequilibrium discharge maintained at atmospheric pressure by continuous microwave gyrotron radiation at 24 GHz was obtained and studied for the first time. It is shown that in the regime of argon discharge stabilization by carbon dioxide flow the temperature of electrons is 0.2-0.3 eV at gas temperature 1200-1500 K and the electron density does not exceed the cutoff value for the heating frequency in a wide power range. Keywords: microwave heating, atmospheric pressure discharge, nonequilibrium plasma, gyrotron.

Разряд атмосферного давления, поддерживаемый миллиметровым излучением в волноводном плазмотроне

In the developed waveguide plasmatron with combined gas influx, a nonequilibrium discharge maintained at atmospheric pressure by continuous microwave gyrotron radiation at 24 GHz was obtained and studied for the first time. It is shown that in the regime of argon discharge stabilization by carbon dioxide flow the temperature of electrons is 0.2-0.3 eV at gas temperature 1200-1500 K and the electron density does not exceed the cutoff value for the heating frequency in a wide power range.

The generalized method for estimating reserves of shale gas and coalbed methane reservoirs based on material balance equation

As the main unconventional natural gas reservoirs, shale gas reservoirs and coalbed methane (CBM) reservoirs belong to adsorptive gas reservoirs, i.e., gas reservoirs containing adsorbed gas. Shale gas and CBM reservoirs usually have the characteristics of rich adsorbed gas and obvious dynamic changes of porosity and permeability. A generalized material balance equation and the corresponding reserve evaluation method considering all the mechanisms for both shale gas reservoirs and CBM reservoirs are necessary. In this work, a generalized material balance equation (GMBE) considering the effects of critical desorption pressure, stress sensitivity, matrix shrinkage, water production, water influx, and solubility of natural gas in water is established. Then, by converting the GMBE to a linear relationship between two parameter groups related with known formation/fluid properties and dynamic performance data, the straight-line reserve evaluation method is proposed. By using the slope and the y -intercept of this straight line, the original adsorbed gas in place (OAGIP), original free gas in place (OFGIP), original dissolved gas in place (ODGIP), and the original gas in place (OGIP) can be quickly calculated. Third, two validation cases for shale gas reservoir and CBM reservoir are conducted using commercial reservoir simulator and the coalbed methane dynamic performance analysis software, respectively. Finally, two field studies in the Fuling shale gas field and the Baode CBM field are presented. Results show that the GMBE and the corresponding straight-line reserve evaluation method are rational, accurate, and effective for both shale gas reservoirs and CBM reservoirs. More detailed information about reserves of shale gas and CBM reservoirs can be clarified, and only the straight-line fitting approach is used to determine all kinds of reserves without iteration, proving that the proposed method has great advantages compared with other current methods.

Wellbore multiphase flow behaviors of gas kick in deep water horizontal drilling

During the deepwater drilling, the complicated gas-liquid-solid multiphase flow will occur if the formation gas enters and migrates in the wellbore. Through understanding of the wellbore flow behaviors is of great importance for the blowout prevention and well control. Considering the dynamic mass and heat transfer process in wellbore caused by alternating ambient temperature field, a multiphase flow model of multicomponent fluid in wellbore is deduced and developed, including the continuity equation, momentum conservation equation and energy conservation equation. Furthermore, the corresponding initial and boundary conditions are proposed for different working conditions in deepwater drilling, and an efficient numerical solution method is established, including dynamic mesh generation method and discrete solution method of partial differential equations. Applied in a deep-water kicking well, the proposed model is used to analyze the multiphase flow rules in the wellbore. The results show that in the process of annular fluid returning from the bottomhole, the pressure generally decreases linearly, while the temperature change is nonlinear. The temperature first rises and then falls at the formation section, and first falls and then rises at the seawater section. Furthermore, the pit gain increases approximately in a quadratic polynomial relationship, caused by the rise and expansion of gas in the wellbore, and the pressure drop and gas influx rate increase at the bottomhole. In the process of kick evolution, the standpipe pressure and bottomhole pressure gradually decrease, which can be an important sign for kick detection.

Flowback rate-transient analysis with spontaneous imbibition effects

Analysis of flowback data, gathered immediately after fracture stimulation, can be performed to understand the fluid flow physics, investigate flow regimes, and obtain early estimates of fracture properties. During a hydraulic fracturing treatment, significant amounts of fracturing fluid will leak-off from the fractures into the reservoir due to Darcy flow, capillary, osmotic and electrostatic forces. Capillary invasion of fluids into the reservoir can cause a loss in gas relative permeability, leading to an altered zone near the fracture-matrix interface, therefore impeding the flow of hydrocarbons into the fracture. Due to this phenomenon and other fluid transport mechanisms, a simple application of Darcy's law might not be adequate for describing the fluid flow physics when solid-liquid interaction is significant. To overcome some of the above limitations, spontaneous imbibition effects are modeled at the fracture/matrix interface during the flowback period in this study.This paper presents a semi-analytical model for analyzing two-phase water and gas flowback data, when spontaneous imbibition occurs. This model was developed by solving the fracture and reservoir matrix flow equations simultaneously. The effects of fracture and reservoir matrix pressure gradients on gas and water influx at the fracture-matrix interface are accounted for in order to evaluate the reservoir matrix hydrocarbon influx. The proposed model accounted for spontaneous imbibition driven by capillary forces by quantifying the fluid influx due to capillary processes and adding it to the mass flow equations. Further, capillary pressure effects were incorporated into the PVT properties of matrix pseudovariables. The average phase pressures in the fracture and matrix were calculated iteratively using a modified material balance approach.The proposed semi-analytical model was successfully verified using fully-numerical simulation data. Practical application of the proposed model was then demonstrated using production data from a multi-fractured horizontal well.

Combining Knowledge and a Data Driven Method for Identifying the Gas Kick Type in a Fractured Formation

The main forms of gas kicks into the wellbore during drilling in fractured carbonate reservoirs are underbalanced pressure and gravity displacement. These two forms of gas kicks have different mechanisms of gas entry into the wellbore and different well control measures, which require the timely identification of the type of gas kick when it occurs. A two-phase flow model with a wellbore-formation coupling was developed, based on the gas kick rate models. The variation characteristics of the bottomhole gas influx rate, the wellbore free gas, the bottomhole pressure, the bottomhole pressure change rate, the pit gain and the outlet flow rate during an underbalanced pressure gas kick and a gravity displacement gas kick, were compared and analyzed. Combining the dynamic time warping (DTW) and the wellbore-formation, coupled with a two-phase flow model, an identification method of the gas kick type, based on the DTW was proposed. Following the detection of the gas kick, the identification is performed by calculating the DTW distance between the surface parameter time series, obtained from the two-phase flow simulation and the surface parameter time series, measured in real time. The field example results show that the method can identify the type of gas kick, based on the real-time surface measurement parameters and provide a basis for taking targeted well control measures.

Effect of faulting on diagenetic processes in the silicate-sulfate-carbonate system: A case study from the Bonan Sag of Jiyang Depression, Bohai Bay Basin

Many extraordinary cements, including mosaic dolomite, poikilitic celestine–barite, anhydrite and chemically zoned saddle-formed dolomite–ankerite, were observed in a reservoir sandstone unit underlying an evaporite sequence in the northern Bonan Sag, which is a saline lacustrine rift basin in the Jiyang Depression of Bohai Bay Basin, China. A suite of petrologic and chemical methods, including optical observation with cathode luminescence, fluid inclusion with laser Raman spectroscopy, X-ray fluorescence, and stable isotopes of carbon, oxygen and sulfur, were carried out. The results suggest that these extraordinary cements are mainly distributed near a fault zone and related to episodes of faulting events. Fault rupturing at shallow burial depths resulted in the dislocation of the evaporites and sandstones and made it possible for an influx of alkaline fluid from evaporites into the fault zone, where mosaic dolomite precipitated, and near fault reservoir units, such as where celestine–barite precipitated. Within the ‘oil window’, the reactivated normal faults, which induced a pressure drop in the reservoir unit, may have resulted in gas influx (e.g., CO2 and H2S) and hydrocarbon charging, enhancing K-feldspar dissolution and cementation of assemblages of quartz, albite and illite. The cyclic fault rupturing and sealing in this setting probably resulted in repeated ‘openness’ of the diagenetic system, chemical perturbation of the pore fluids (e.g., pH dropping and returning), and cyclic dissolution–regrowth within the silicate–sulfate–carbonate diagenetic system. This study may highlight the awareness of diagenetic complexity in fault zones and shed light on reservoir evaluation in rift settings.

Geophysical evidence for submarine methane seepage on the Western slope of Okinawa Trough

Identifying seafloor methane seepage efficiently has important implications for assessing environmental impact, reducing the uncertainty of top seal integrity, understanding the petroleum system, and mitigating the drilling hazards due to shallow gas influx. Pore water geochemistry analyses suggest that the study area has an extremely high methane seepage flux and active methane anaerobic oxidation processes. However, geochemical data cannot provide details about the internal seepages. The geophysical dataset from the Western slope of Okinawa Trough, including 2D high-resolution seismic, sub-bottom profiles, and bathymetry, gives us a good opportunity to understand the detailed characteristics of methane seepages in this study. Geophysical data have revealed numerous methane seepage-related features such as seismic chimneys, pockmarks, submarine domes, and amplitude anomalies, including bright spots and enhanced reflections. Pockmarks and domes are often associated with seismic chimneys, indicating that fluid migration is important in their formation. The various geophysical expressions may represent different stages of methane seepage. Fluid quickly drains, causing severe sediment deformation and forming pockmarks, whereas domes may indicate the early stages of fluid discharge. Chimneys that do not extend to the seafloor may indicate that the venting is gradual and focused. Flares linked to domes or pockmarks may indicate that the fluid migration is active. Several factors triggered the existence of methane seepages on the Western slope of the Okinawa Trough, including tectonic setting, overpressure and rapid sedimentation.

A dynamic event tree for a blowout accident in an oil deep-water well equipped with a managed pressure drilling condition monitoring and operation system

Blowout is one of the most dreaded accidents for Oil and Gas companies. It is of particular concern during the drilling phase of deep-water oil & gas wells. This is due to the largely uncertain and extremely harsh environmental conditions that affect the design, drilling and operation activities of these wells. Seeking new technological solutions to prevent blowout has led, in the last few decades, to develop Managed Pressure Drilling (MPD) techniques.MPD offers many advantages compared to conventional drilling techniques, such as the capability (1) to detect the gas influx that initiates the kick that might lead to blowout and (2) to optimally control and circulate out this influx, to avoid the blowout. Nevertheless, effects of uncertainties on the MPD functionality are not fully understood and satisfactorily modelled within conventional safety assessment that relies on Event Trees (ETs).In this work, we propose a Dynamic Event Tree (DET) modelling framework of the scenario of kick escalation into blowout to allow accounting for the uncertainties that affect not only the kick variables, but also for the fundamental role played by the time and the delay of the kick detection task. The uncertainties affecting the kick variables are evaluated from kick events records taken from 2000 oil wells drilled in the Niger Delta, whereas the uncertainties affecting the time and delay of kick detection are evaluated by simulating the performance of the tool embedded into the MPD for kick detection (which applies the CUSUM statistical test to differential flow measurements), and assuming a possibilistic distribution for the confirmation time needed by the operator to take counteracting measures with respect to the evolving accidental scenario.A Hybrid Monte Carlo and Possibilistic method is utilized to represent and propagate uncertainties associated to the events occurring throughout the DET. Results are compared with those of a Purely Probabilistic method in support of the blowout probability quantification.

ГЕОДИНАМІКА

The purpose of the research is to analyze the impact of the region's geodynamics on the formation of hydrocarbon reservoirs in the carbonate Lower Visean-Tournaisian stratum. The paper is focused on the substantiation of hydrocarbon traps within the Machukhy-Tyshchenky area of the southern zone of the Dnieper-Donets basin, as well as oil and gas exploratory drilling and new effective methods of stimulating gas inflows to boreholes. Methodology. The study applies the stratigraphic, lithological, tectonic, paleotectonic methods of studying geology and oil potential, as well as the method of geological analogies. Results. Gas-bearing carbonate rocks of the Early Visean-Tournaisian age in the Machuhy-Tyshchenky area have been studied. A comparison with other oil and gas regions has shown that they are the domes of carbonate platforms (Wаulsoгtiаn facies). Three echelons of bioherm limestones have been identified within the the area. The research helped to describe the stages of their formation and determine the dependence of reservoir properties of limestones on their biofacial types. The role of tectonic fracture in the formation of reservoir rocks is shown. As a rule, tectonic fractures are cemented by calcite under the action of formation waters. An assumption is made about the formation of microfractures in dense limestones due to the action of plumectonic. It consists in the intrusion of high-energy fluids from the depths of the earth, the natural fluid fracturing of rocks and the formation of non-anticlinal hydrocarbon accumulations in them. Probable places of fluid breakthrough may be zones of deep faults: the Ingulets-Kryvorizhzhya-Krupetsk fault zone crosses Machuhy-Tyshchenky area. Filling microfractures with hydrocarbons prevents their cementation. The paper gives examples of microfracturing in the cores of boreholes and establishes reduced core from microfracture intervals. To identify microfracturing intervals in carbonate rocks, it is proposed to use information on the reduction of core, as well as the speed drilling of rocks. The study suggests using multistage hydrofracturing and acid hydrofracturing in order to stabilize and increase gas influxes from carbonate reservoirs to the boreholes. Such technology should provide the connection between the borehole and oil-saturated reservoirs. Probable factors of negative impact on the environment during hydrofracturing have been identified. Originality. Adiabatic microfracturing of dense lithotypes of rocks is possible at considerable depths, in addition to tectonic fracturing. It is due to natural fluid fracturing of sedimentary strata by hydrocarbon gases. This gives hope for the discovery of new types of hydrocarbon deposits that are not associated with anticline traps. Practical significance. Geophysical surveys and the location of six boreholes are recommended in order to search for hydrocarbon deposits in the Machuhy-Tyshchenky area. The study suggests effective methods for increasing gas influxes to boreholes from low-permeability carbonate rocks.

Effect of Oil Viscosity on Flow Pattern Transition of Upward Gas-Oil Two-Phase Flow in Vertical Concentric Annulus

Summary Gas-oil two-phase flow usually occurs during gas influx into the wellbore annulus of deepwater drilling with oil-based drilling fluid or gas-oil production from the wellbore annulus. A flow pattern transition often is used in well control or in production parameter design. Related studies primarily have focused on gas-water two-phase flow, which is significantly different from gas-viscosity oil two-phase flow. We conducted experiments on a facility that included a flow section that was 13 000 mm long, with a 60-mm inner pipe and a 100-mm outer pipe in the annulus. A range of oil viscosities from 16 to 39 mPa∙s has been studied. The superficial gas and oil velocities varied from 0.55 to 17.077 m/s and from 0 to 0.414 m/s, respectively. A flow pattern was identified based on visualized analysis using electrical capacitance volume tomography (ECVT) and void faction wave analysis. Flow pattern maps of different viscosities were plotted based on measured data. Transition criteria based on Froude number and Archimedes number were established. The new model was compared with gas-water two-phase flow transition models and validated with experimental data. The effect of viscosity on flow pattern transition was revealed. The transition boundary of the bubble to slug flow and slug to churn flow both moved in the direction of smaller superficial gas velocity with an increase in oil viscosity. There may exist a critical viscosity value when churn flow transited to annular flow. When the viscosity was lower than this critical point, the above result was the same for churn to annular flow when the superficial oil velocity was low. With an increase in the superficial oil velocity, however, the boundary gradually changed to high superficial gas velocity as the oil viscosity increased. When the viscosity was larger than the critical point, the oil viscosity had a slight influence on the transition.

Influx of radioactive gas in norm occurrences in Northeastern Brazil

Radon and progeny are potentially relevant in radioecological studies, as they contribute more than half of the exposure to environmental radiation. The investigation of 222Rn in internal environments of municipalities of Paraíba and Rio Grande do Norte in Brazil was carried out using passive dosimetry with α Espec-222, installed in environments selected by the history of natural radiative occurrences. The monitoring time was eight months to consider seasonal influence. Concentrations from 26.91 to 316.35 Bq m-3 were obtained, with a maximum effective dose of almost 8 mSv y-1. The influence on households exceeds, by almost 31%, the average obtained for occupational environments. The municipalities of Paraíba presented higher results for Rn, with an average of almost 176 Bq m-3 and an effective dose greater than 4 mSv y-1. The application of individual occupancy factors for home and work environments made it possible to combine the dosimetric models, making the scenario closer to the real exposure of individuals who work and reside in the same municipality, with a dosimetric response of 21.45% lower than the model used worldwide. The different scenarios applied allowed expanding the radiometry of the environments, generating a database that precedes studies of environmental and radioecological impacts, strengthening security and enabling new works to interpret public health problems in search of joint and shared solutions.

Geological features of gas-condensatedeposits with additional increase of gas reserves

The purpose of the work is to elucidate general peculiarities and characteristic features of geological conditions for the occurrence and development of gas-condensate fields of the Dniprovsko-Donetskyi depression (DDD), on which the growth for the gas reserves is obtained with the further use of these indicators as forecast-estimated. The methods. The age of industrial horizons, a type of reservoir, a type of deposit, the presence of salt deposits, a depth of deposit roof, a deposit regime, levels of gas-bearingness, calculated thickness of reservoirs and their total thickness at the field, the initial formation pressure, initial gas reserves, volumes of excess of initial gas reserves were determined; the maximum geostatic pressure was calculated, the minimum reservoir gas pressure until its growth jump or stabilization was established; the value of the compression pressure for the reservoir of deposits was calculated and the relationship between the effective pressure in the deposit and the strength of the porous sandstone-reservoir was established; the common features and characteristics for the geological conditions of gas condensate field (GCF) with additional resources were undertaken, among which the predictive and estimated indicators were selected. Findings. The authors carried out a detailed analysis of the well-known gas and gas condensate fields of Ukraine. Gas-condensate deposits of the Mashivsko-Shebelynskyi gas-bearing area of the Dniprovsko-Donetskyi depression (DDD) are chosen as an object of the research. It has been established that the power of the gas column, the structure area, and the total power of productive horizons characterize the promising volume of the gas-bearing structure, which allows approximately give a predictive quantitative assessment of the production of additional gas reserves. Attracting additional gas volumes is due to the gas influx from newly made technogenic collectors, which were formed under the action of a geomechanical factor in the process of long-term development of the field. The formation of technogenic collectors occurred due to the compression of the main reservoir, the deformation of the rock strata, and the decomposition of the overlying rocks, the development of the crack propagation, permeability increase and gas recovery rising. The originality. It has been established that the power of the gas column, the structure area, and the total power of productive horizons characterize the promising volume of the gas-bearing structure, which allows approximately give a predictive quantitative assessment of the production of additional gas reserves. Practical implimintation. The geomechanical factor management opens up the prospect of obtaining additional industrial gas influx in the late stages of the development of gas and gas-condensate fields, by predicting the geological conditions for the formation of improved secondary filtration and capacitive properties favorable to form technogenic gas deposits.

Flow regulation and bottom hole pressure control under gas influx condition based on RMR system

During the drilling process of RMR system, when the gas reservoir is drilled, the bottom hole pressure and formation pressure are in an unbalanced state, and the formation fluid invades the bottom hole under the action of pressure difference, further causing complex situation such as overflow and kick. In order to effectively control the bottom hole pressure during drilling and ensure drilling safety, a bottom hole pressure calculation model of RMR system under gas influx condition is established based on the gas-liquid two-phase flow theory. Three flow regulation methods of increasing the outlet flow of drilling pump and subsea pump at the same time, reducing the outlet flow of subsea pump while the outlet flow of drilling pump remains unchanged, and increasing the outlet flow of drilling pump while reducing the outlet flow of subsea pump are selected to dynamically simulate the change process of bottom hole pressure after flow regulation. Through data fitting, The relationship equation between them and bottom hole pressure is obtained, and the flow regulation method of RMR system when controlling bottom hole pressure under gas influx condition is formed.

Modeling and simulation of non-isothermal three-phase flow for accurate prediction in underbalanced drilling

The present study aims at investigating the effect of temperature variation due to heat transfer between the formation and drilling fluids considering influx from the reservoir in the underbalanced drilling condition. Gas-liquid-solid three-phase flow model considering transient thermal interaction with the formation was applied to simulate wellbore fluid to calculate the wellbore temperature and pressure and analyze the influence of different parameters on fluid pressure and temperature distribution in annulus. The results show that the non-isothermal three-phase flow model with thermal consideration gives more accurate prediction of bottom-hole pressure (BHP) compared to other models considering geothermal temperature. Viscous dissipation, the heat produced by friction between the rotating drilling-string and well wall and drill bit drilling, and influx of oil and gas from reservoir have significant impact on the distribution of fluid temperature in the wellbore, which in turn affects the BHP. Bottom-hole fluid temperature decreases with increasing liquid flow rate, circulation time, and specific heat of liquid and gas but it increases with increasing in gas flow rate. It was found that BHP is strongly depended on the gas and liquid flow rates but it has weak dependence on the circulation time and specific heat of liquid and gas. BHP increase with increasing liquid flow rate and decreases with increasing gas flow rate.

Computationally efficient simulation of non-isothermal two-phase flow during well construction using a new reduced drift-flux model

• A novel reduced drift-flux model for non-isothermal two-phase flow is developed. • This model considers transient heat transfer and gas-in-oil solubility behavior. • This model shows higher accuracy compared to historical reduced drift-flux models. • This model runs two orders of magnitude faster than real-time. • This model is validated using both field data and benchmark models. Two-phase flow modeling is important in well construction field for well planning and real-time applications. In this paper, a new non-isothermal two-phase flow model is presented that improves upon the simulation accuracy and capability of historical reduced drift-flux models (RDFM) while still retaining high computational efficiency. Built on the “no pressure wave” assumption of the RDFM, our new RDFM achieves improvements through calculating the temperature dynamics, considering interface mass transfer (i.e., gas-in-oil solubility behavior), and introducing a new lumped pressure dynamics model. By including these physical factors that are critical for practical applications, the proposed RDFM shows higher simulation accuracy and capability compared to historical RDFMs. The validity of the proposed model is proven by comparing it to field measurements, benchmark models, and the classical drift-flux model. Moreover, the proposed RDFM successfully retains the high computational efficiency of historical RDFMs even with the addition of the aforementioned complex physical dynamics. When conducting full-scale gas influx simulations, the proposed RDFM achieves a computational speed at more than two orders of magnitude faster than real-time. Due to its good performance on both computational efficiency and simulation accuracy, the proposed model is suitable for real-time applications in most well construction scenarios. It is especially superior to historical RDFMs when simulating more complicated but still common scenarios, e.g., deepwater wells drilled in high-pressure high-temperature environments, and wells experiencing gas-in-oil solubility behavior.

Underground in-situ investigation of spatial and temporal changes of rock salt integrity in the marginal area of a natural CO2-rich cavernous structure

In this paper, we present an in-situ study of the marginal area of a CO2- and brine-rich cavernous structure in an underground rock salt mine. To reveal sources and dynamics of fluid movement, the temporal and spatial distribution of fluids in the potentially weakened cavern rim in salt were investigated. Seismic imaging, followed by long-term gas monitoring were applied along a transect from the cavernous structure to the undisturbed rock formation. The underground seismic survey comprised travel time tomography and pre-stack depth migration and showed, in agreement with the results of gas monitoring, disturbed areas without correlation to the cavernous structure. During two years, the monthly gas inflow into isolated borehole sections revealed insights into short term changes of gas migration pattern in rock salt. The measurements showed gas influx of up to 4 kPa/day and CO2 concentrations of up to 1.2%, especially during the beginning of the campaign. The gas migration is coupled to discrete fracturing and was observed to be spatially and temporary confined. Overall, no correlation between gas occurrences and their distance to the cavern exists, suggesting no wide-ranging fluid-rock interaction in the rim of the investigated natural cavernous structure in rock salt. The occurrence of gas is coupled to spatially and temporary limited fracturing which evidently healed and regained rock salt typical tightness.