Formation Pressure Inversion Method Based on Multisource Information

Summary The exploration and development of offshore oil and gas have greatly alleviated the tension of global oil and gas resources. However, the abnormal pressure of offshore reservoirs is more common compared with terrestrial oil and gas reservoirs, and the marine geological structure is complex, with the development of faults, fractures, and high and steep structures, which leads to the strong anisotropy of formation pore pressure distribution and uncertainty of pressure system change. In this paper, considering the corresponding characteristics of the randomness of the formation pressure prediction results in the Eaton equation for their respective variables, a formation pressure inversion method based on multisource information, such as predrilling data, bottomhole while drilling data, seabed measured data, and surface measured data, is established. On this basis, combined with the data of a well in the South China Sea, the variation law of the uncertainty of formation pressure prediction results under the conditions of predrilling data, measurement while drilling (MWD) data, and their mutual coupling is analyzed. The simulation results show that the uncertainty distribution of formation pressure prediction based solely on predrilling data shows linear accumulation trend with well depth, and the formation pressure inversion method based on multisource information can significantly curb the increasing trend of uncertainty when MWD data are introduced. Therefore, through the analysis of typical change patterns of monitoring parameters under normal/abnormal conditions during drilling, combined with the method of multisource information, the abnormal pressure information can be accurately predicted and inversed, which provides important support for wellbore pressure regulation under complex formation conditions.

Development of a Weighted Barite-Free Formate Drilling Mud for Well Construction under Complicated Conditions

Construction of oil and gas wells at offshore fields often involves high formation pressure and the presence of swellable clay rocks in the section. In addition, productivity preservation is also an important aspect. For this purpose, it is necessary to reduce the solids content of the drilling mud. The purpose of this work is to develop, improve, and study compositions of weighted drilling muds with low content of solids, on the basis of organic salts of alkali metals and polymers for the construction of wells prone to rock swelling and/or cavings, as well as drilling fluids for drilling-in the formation. In order to achieve the set goal the following is required: Analysis of existing drilling muds of higher density for drilling wells in unstable rock intervals and for drilling in the productive formation; analysis of experience in using drilling systems on the formic acid salts base and substantiation of requirements for flushing fluids during well construction; development and investigation of drilling mud compositions on the formate base; and the evaluation of inhibiting effect of systems containing organic salts, polymer reagents, and calcium carbonate on clay samples. The developed drilling mud is characterized by a high inhibiting ability that allows minimized mud-weighting by the natural solid phase. This reduces the volume of prepared mud and facilitates the regulation of its properties by reducing the dispersion of drilled cuttings; it eliminates problems related to hydration and the swelling of active clay rocks; and stabilizes unstable argillites prone to caving. The low solids content, low filtration rates, and inhibitory nature of the mud allows high stability of the rheological properties of the mud, and preserves oil and gas reservoir productivity under conditions of elevated formation pressure.

Using Seismic Data to Predict Shale Pore Pressure and Overpressure Sweet Spots: A Case Study from the Lower Silurian Longmaxi Formation in Sichuan Basin, China

Practices of marine shale gas exploration and development in south China have proved that formation overpressure is the main controlling factor of shale gas enrichment and an indicator of good preservation condition. Accurate prediction of formation pressure before drilling is necessary for drilling safety and important for sweet spots predicting and horizontal wells deploying. However, the existing prediction methods of formation pore pressures all have defects, the prediction accuracy unsatisfactory for shale gas development. By means of rock mechanics analysis and related formulas, we derived a formula for calculating formation pore pressures. Through regional rock physical analysis, we determined and optimized the relevant parameters in the formula, and established a new formation pressure prediction model considering P-wave velocity, S-wave velocity and density. Based on regional exploration wells and 3D seismic data, we carried out pre-stack seismic inversion to obtain high-precision P-wave velocity, S-wave velocity and density data volumes. We utilized the new formation pressure prediction model to predict the pressure and the spatial distribution of overpressure sweet spots. Then, we applied the measured pressure data of three new wells to verify the predicted formation pressure by seismic data. The result shows that the new method has a higher accuracy. This method is qualified for safe drilling and prediction of overpressure sweet spots for shale gas development, so it is worthy of promotion.

A Success Story of Critical Data Gathering During the Development Phase of Extreme ERD Well Drilling

This paper discusses a holistic combination of advanced formation evaluation techniques with pressure testing and reservoir navigation services to mitigate uncertainty related challenges in real time and successfully drill & place ERD laterals targeting Jurassic carbonate reservoirs. A meticulously planned approach to navigate the well trajectory by tracking the desired properties, informed decision-making while drilling and accurate data acquisition for aiding appropriate selection and placement in-flow control device (ICD) in lower completion design and future reservoir management contributed to the success of these complex wells in carbonate reservoirs. The first well in this study, involved drilling and evaluating a long lateral section as single oil producer targeting a carbonate reservoir. While no tar presence was expected, a combination of density, neutron porosity and nuclear magnetic resonance (NMR) logs while drilling resulted in identifying a deficit NMR porosity when compared to density porosity. Deployment of a formation pressure testing while drilling (FPWD) tool enabled measurement of the formation mobility and validate the presence of a tar. Using the same combination of measurements in the subsequent wells for delineating the tar enabled accurate planning of injection wells on the periphery of the field. Approximately 3 days were saved compared to the first well where the drill string had to be POOH to run-in with FPWD service. Hence, having FPWD tool in the same string helped in confirming the formation mobility in real time to call for critical decision making like changing the well trajectory or calling an early TD. Across all the wells drilled in this field, the formation pressure, mobility and porosity measurements provided valuable input for optimum ICD placement and design. Successful identification of unexpected tar resulted in substantial rig time savings, accurate planning of asset utilization and added confidence in design and placement of lower completions by utilizing LWD data. Benefits of integrated data and services combination became clear for applications involving advanced reservoir characterization and enhanced well placement in complex carbonate reservoirs. From the offset wells, a tar was seen in deeper formations but the integration of LWD NMR and mobility data from this well confirmed the presence of a tar within the zone of interest. The study established a cost-effective workflow for mitigating uncertainties related to tar encountered while drilling extreme ERD laterals in an offshore environment where any lost time results in significant increase in expenditures during the development phase. A systematic approach to tackle these uncertainties along with acquisition of critical data for the design & placement of completion results in optimum production from the reserves.

Taming the Thunder Horse With Axes and Vectors

The Thunder Horse Field targets Middle Miocene deepwater turbiditic reservoirs. Despite being prolific, the mapping of the ~180 m thick, partly amalgamated reservoir sandstones is challenging. Seismic quality is reduced by the presence of salt structures. The salt overburden and high formation pressure require the use of heavy mud weights and oil-based drilling fluids, which limit the resolution and interpretation potential of borehole image logs (BHI). Halokinetic movements caused significant post-depositional deformation of the already complex gravity-driven sediment stack, and the reservoir beds drape against an E-W oriented salt wall. Consequently, the assessment and removal of the structural dip component are not trivial, and the evaluation of paleo-transport directions is considerably more complicated compared to undisturbed deepwater reservoirs. This paper illustrates the potential of eigenvector methods to BHI from Ruehlicke et al. (2019) for reconstructing the depositional slope and the architecture of mass transport complexes in the case of chaotic depositional settings and uncertain structural dip. Figures from Henry et al. (2018) are used wherein part axial analysis was performed on data from a group of Thunder Horse wells and presented in more detail.

Experimental study on production performance and reserves utilization law in carbonate gas reservoirs

Carbonate gas reservoirs in China are rich in reserves. In the development process, there are many reserves with low permeability, low efficiency and low recovery degree. It is difficult to stabilize gas well production and prolong its life cycle. Under the condition of original water saturation (Sw) of 0%, 20%, 40%, 55% and 65%, respectively, the physical simulation experiment of gas reservoirs depletion development was carried out by using long core multi-point embedded pressure measuring system. The long cores with average gas permeability of 2.300 mD, 0.485 mD and 0.046 mD (assembled from 10 carbonate cores) were used to carry out this experiment. During the experiment, the pressure dynamics at different positions inside the long core and the gas production dynamics at the outlet were recorded in real time to reveal the production performance and reserves utilization law of carbonate gas reservoirs. The results show that the stable production period of tight reservoir in carbonate gas reservoirs is short, and the low production period is relatively long. The stable production time and recovery rate of gas reservoir increase with the increase of reservoir permeability and decrease with the increase of water saturation. The production of tight carbonate gas reservoirs with permeability less than 0.1 mD is greatly affected by pore water, and the reservoir pressure distribution shows a steep pressure drop funnel, and the reserves far from well are rarely used. Therefore, the reserves far from well should be utilized by closing well to restore formation pressure balance, densifying well pattern or transforming reservoir. The variation range of water saturation in the development of carbonate gas reservoirs is influenced by reservoir permeability and water saturation, and closely related to formation pressure gradient in production process. It decreases with the increase of reservoir permeability and increases with the increase of original water saturation. The research results provide a theoretical basis for understanding the relationship between physical properties of carbonate gas reservoirs and production performance, reserves utilization law, and realizing balanced utilization, efficient development and long-term stable production of carbonate gas reservoirs.

Comparison and adaptability evaluation of formation pressure calculation methods and computer simulation in Jingbian gas field

In the process of oilfield development, formation pressure is an essential parameter for evaluating oilfield development effect, calculating dynamic geological reserves, conducting daily dynamic analysis of oil and water Wells and predicting oilfield performance. The pressure recovery time of conventional gas well after shut-in is very long, and it is difficult to effectively carry out targeted implementation due to the influence of gas field external supply task. In this paper, based on the actual data of Jingbian gas field, through the comparison of several calculation methods of formation pressure, the best method to calculate formation pressure is comprehensively screened out. The results show that: ①For a single method, the accuracy of the method from high to low is the well head casing pressure conversion method, the pressure drop curve method, the binomial productivity equation method, and the quasi-steady state mathematical model method.②The absolute error of multi-method comprehensive calculation method is 0.9MPa, which is far less than the average absolute error directly calculated by one method. The multi-method comprehensive calculation method is reliable when applied to the formation pressure evaluation of typical gas Wells in Jingbian gas field, which lacks data.

Development of blocking compositions with a bridging agent for oil well killing in conditions of abnormally low formation pressure and carbonate reservoir rocks

Production well killing before workover operations in late-stage oil and gas-condensate fields can be complicated by abnormally low formation pressure, carbonate type of reservoir rocks, and high gas-oil ratio. These complications lead to the intensive absorption of technological fluids by the formation and gas ingresses, which, in its turn, increases the time of killing wells and putting them on production, reduction of productivity, and additional costs. Therefore, it is crucial to develop a high-performance well-killing composition that would allow improving the efficiency of killing wells in complicated geological, physical, and technological conditions at the expense of reliable overlapping of the perforation interval (or open wellbore) to prevent gas intakes and gas outflow from the formation. To develop blocking compounds, a set of laboratory tests has been carried out, including physical and chemical (determination of density, viscosity, thermal stability, sedimentation stability, etc.) and research of blocking and filtration properties of compositions during simulation of a fractured reservoir. In the course of laboratory tests, the choice of fractional composition and polymer filler concentration was substantiated in the blocking emulsion and polymer compositions to increase the efficiency of their application under the complicated conditions of killing oil wells. As a result of laboratory research and field tests, the emulsion and polymer blocking compositions containing bridging agent (microcalcite) were developed, which increase the oil well killing efficiency by preventing the absorption of technological fluids in the formations and, as a result, preserving its productivity.

DEVELOPMENT OF OİL PRODUCTİON IMPROVEMENT TECHNOLOGY

It is important to conduct research without storing wells. Prior to this study, the wells will be shut down to explore the wells and additional work will be done for the survey. The research work itself took 15-20 days, using this research to determine the necessary parameters for the joint operation of the reservoir in a short time. In solving engineering problems, the force often applied to the system is to determine its reaction. In such cases, the correct answer to the question can be obtained on the basis of theoretical calculations. However, this is not always possible, and in some cases, instead of a mathematical model of the object under study, research is conducted to find a similar one. An electrical circuit can be thought of as a similar model of the mechanical oscillations of a solid. Therefore, by studying the motion of an electric charge in an electric circuit, it is possible to apply the oscillations of a mechanical system and the distribution of pressure in a porous medium by studying the distribution of heat in an object. If the final results of the two events are similar, then the modeling can be performed. The formation is considered as a working machine to determine the similarity of the drainage zone of the oil and gas well. In this case, the fluid system is lifted by lifting pipes to a certain height with formation pressure and the production of the well is ensured. As a result of the research, it was found that the mode of operation of the drainage zones of the strata in the wells is close to the mode of operation of centrifugal electric pumps. Keywords: debit, formation pressure, gas flow rate, drainage zone of the well, hydraulic characteristics of discharge line, bottomhole pressure, stress on discharge line of the pump.