Zhang, Yingchun (CNOOC Research Institute Co., Ltd.) | Xu, Wei (CNOOC Research Institute Co., Ltd.) | Zou, Jingyun (CNOOC Research Institute Co., Ltd.) | Jing, Zhiyi (CNOOC Research Institute Co., Ltd.) | Fang, Lei (CNOOC Research Institute Co., Ltd.) | Liu, Jun (CNOOC International Limited)
In complex clastic reservoirs, deviation often exists in oil saturation derived from logging interpretation due to the borehole conditions and log quality. Especially in thin-sand reservoirs, oil saturation is generally lower than actual results because of boundary effect. An innovative approach of saturation height function coupled with rocktype is provided to improve the accuracy of saturation prediction in well logs and spatial distribution. The model results are compared with log derived results.
The new approach is based on the routine and special core analysis of over 100 core samples from the complex clastic reservoir in the north of Albert Basin in Uganda. Discrete rocktypes (DRT) are determined by flow zone index and pore throat radius which indicate the fluid flows. After converting the capillary pressure (Pc) data to reservoir conditions, Lambda curve fitting (Sw = A * PcB + C) is used to fit each capillary pressure curve. Then, a robust relationship between the fitting coefficients (A, B, C) and rock properties (i.e. porosity and permeability) is expressed as a nonlinear function for each DRT. Combined with the height above free water level, a water saturation (Sw) model is constructed by SHF within DRT model.
Using the porosity and permeability obtainedfrom routine core analysis, FZI and pore throat radius are calculated (e.g., by Winland function). Five different rocktypes (DRT1-5) are defined in the delta sand reservoir in the north of Albert Basin with distinct pore textures. The distinguishment is in accordance with the shape of capillary pressure curve, that is, the flow capability increases from DRT1 to DRT5. A strong correlation between Pc and Sw processed by Lambda curve is acquired for each core sample. Meanwhile, 3 coefficients A, B and C can be obtained in Lambda formula. By nonlinear regression, coherent relation between each factor and reservoir properties (porosity and permeability) for each DRT are obtained. Height above the free water level is estimated by geometrical modeling on the oil water contact. The Sw model is constructed by the new SHF function coupled with DRT model. It showed that the water saturation derived from SHF is highly consistent with log derived results and NMR results. Moreover, it provides more precise results in thinner sands and in spatial distribution.
Based on the identified different rocktype, a new SHF derived from capillary pressure data is utilized to establish the relationship between saturation, the height above the free water level and rock properties. The approach can significantly improve the accuracy of saturation prediction of thin reservoir and reasonably depict the spatial distribution characteristics of saturation. Furthermore, the approach will provide a more precise result in hydrocarbon volume calculation and numerical simulation.
This seminar will teach participants how to identify, evaluate, and quantify risk and uncertainty in everyday oil and gas economic situations. It reviews the development of pragmatic tools, methods, and understandings for professionals that are applicable to companies of all sizes. The seminar also briefly reviews statistics, the relationship between risk and return, and hedging and future markets. Strategic thinking and planning are key elements in an organisation’s journey to maximise value to shareholders, customers, and employees. Through this workshop, attendees will go through the different processes involved in strategic planning including the elements of organisational SWOT, business scenario and options development, elaboration of strategic options and communication to stakeholders.
One of the world’s leading energy watchers says the second shale revolution will come in the form of LNG exports. After 70 years of production, more than 30% of the Arab C reservoir stock-tank original oil in place has been recovered through various mechanisms including natural depletion, waterflooding, gas lift implementation, and horizontal-well development. The North field offshore Qatar was observed to have a chance of inner annuli becoming charged with shallow-gas pressure with possible communication to other annuli, which was thought to be a well integrity concern. Airborne imaging spectroscopy has evolved dramatically since the 1980s as a robust remote-sensing technique used to generate 2D maps of surface properties over large areas.
Regulators say the blowout that killed five workers on a Patterson-UTI rig in Oklahoma was the product of a slow-moving series of missed signals, misleading testing, and miscalculations that failed to control a natural gas influx. The new well control rule is evidence that memories of the Macondo blowout remain a powerful force for caution. Despite the rhetoric on both sides of this hot-button issue suggesting big changes, the final changes were incremental. Nonaqueous drilling fluids, such as synthetic-based and oil-based mud (SBM and OBM, respectively), are used frequently to drill one or more sections of a well to reduce drilling problems such as shale sloughing, wellbore stability, and stuck pipe. Three onshore fields in the Emirate of Sharjah, United Arab Emirates, have more than 30 years of production history from more than 50 gas-condensate wells.
Saudi Aramco awarded a contract* to McDermott International for engineering, procurement, constructi ... DNV GL has won a contract to provide independent verification services for Energinet’s section of th ... Equinor has awarded Subsea 7 with an engineering, procurement, construction, and installation (EPCI) ... Malaysian FPSO provider Yinson has secured a long-term contract extension through October 2022 with ... Well-Safe Solutions has been awarded a contract to decommission as many as 21 wells on the DNO-opera ... Infinity Oilfield Services and Medserv have formed a new joint venture named InMedCo to provide a po ... Boskalis Subsea Services said it has been awarded more than £100 million ($126 million) in contracts ... Chevron Australia has awarded Wood with a new contract to provide subsea integration and flow assura ... Qatar Petroleum has awarded McDermott with the FEED contract for the offshore pipelines and topsides ... DOF Subsea has secured two contracts in Brazil. Source: Teekay Offshore Teekay Offshore has agreed to a 3-year contract ... Petrobras has awarded TechnipFMC with an engineering, procurement, construction, and installation (E ... ADNOC awarded a $1.36-billion dredging, land reclamation, and marine construction contract to the UA ... Wood and KBR inked a multimillion-dollar contract to deliver integrated front-end engineering design ... Anadarko Mozambique Area 1, LTDA, a subsidiary of Anadarko Petroleum Corp., named the preferred tend ...
Decisions in E&P ventures are affected by Bias, Blindness, and Illusions (BBI) which permeate our analyses, interpretations and decisions. This one-day course examines the influence of these cognitive pitfalls and presents techniques that can be used to mitigate their impact. Bias refers to errors in thinking whereby interpretations and judgments are drawn in an illogical fashion. Blindness is the condition where we fail to see an unexpected event in plain sight. Illusions refer to misleading beliefs based on a false impression of reality.
The objective of this paper is to present a detailed workflow for developing a field-wide (or basin-wide) “common” equation of state (EOS) model to describe PVT properties1 of all reservoir fluids and wellstream mixtures at all relevant conditions of pressure and temperature. The presented workflow is a result of having developed many field-wide EOS models in conventional reservoirs around the world, and more recently several basin-wide EOS models for North American unconventionals (Eagle Ford, Montney, Bakken, Permian and Scoop/Stack). We address several important considerations in developing a common EOS, as well as when and why a common EOS is needed.
The starting point for developing a common EOS is the use of
Measured PVT data must be scrutinized for quality using a series of consistency checks that include component and phase material balances, cross plots, and continual comparison with EOS results. Using all PVT data from all samples gives a substantial, statistically significant data set that allows trend analysis and outlier identification.
One key to developing a common EOS model is using a sufficient number of components, and proper characterization of heavy fractions that contain varying proportions of the three hydrocarbon groups (paraffin, naphthene and aromatic compounds – PNA). The heavy fractions single carbon numbers C7, C8, C9… and the remaining “residue”, e.g. C36+ are often given average properties that reflect the relative proportions of PNA compounds – i.e. relative paraffinicity (or relative aromaticity). The determination of single carbon number (SCN) and residue properties is what we refer to as heptanes-plus characterization, and it is this characterization that will differ from field to field, or basin to basin.
Sometimes within a given field or basin, the relative paraffinicity may vary so much that a single, common EOS using SCN description is not possible. Two options remain: developing multiple EOS models, or creating a single EOS with some/all heavy fractions having two subfractions – paraffinic and aromatic (e.g. C7P and C7A, C36+P and C36+A). In this latter approach, the P-A split must be estimated, correlated or measured for each fluid mixture, making the approach complicated and less common, but necessary in some fluid systems2.
Developing a common EOS for a field/basin is necessary because in-situ reservoir fluids may vary spatially, change in composition during depletion and gas injection, and because of fluid mixing throughout the production system – within reservoirs, wells, and topside facilities.
For unconventional basins, only a small number of the thousands of wells have laboratory PVT data available, despite significant well-to-well fluid variations – e.g. gas oil ratio (GOR) ranging from 300 to 300,000 scf/STB in the Eagle Ford and Montney basins. Simple PVT correlations are not applicable over the entire range of fluid compositions. Many wells produce complex retrograde condensates, near-critical fluids, and volatile oils that require an accurate and consistent EOS model for estimating PVT properties required by geologic, engineering, and marketing professionals.
Polylactic Acid (PLA) is increasingly used in the oil industry and specifically for diversion in matrix acidizing as evidenced by a number of field cases recently published. The solid polyester is particularly attractive due to its ability to degrade in the presence of water and heat, negating the need for cleanup fluids or complicated procedures. A majority of the analysis on the effectiveness of PLA thus far comprises experiments on artificially created slots, filter cake analysis, and field trials. This paper demonstrates the effect of PLA in wormholes developed by acidizing outcrop cores.
In these experiments, a wormhole is generated in a portion of the core by limiting the amount of acid injected. Next, the PLA is injected into the core using a heavy brine suspension. Finally, more acid is injected until a wormhole breaks through the core. Computer Tomography (CT) scans are taken, and the pressure drop across the core is recorded at each stage. Experiments were conducted for a variety of initial wormhole lengths.
It can be difficult to suspend PLA while injecting it through a core in a way that is benign to the core, acid, and PLA; and in a way that does not add any pressure drop or diversion due to viscosity changes. This paper describes and justifies a suitable method of keeping PLA suspended to allow its use in core flood experiments. The CT scans show that even when the PLA plugs the wormhole, additional acid tends to continue to develop the dominant wormhole. The pressure drop profiles show that the pressure drop due to PLA injection is proportional to the mass of PLA, both in the wormhole and on the core surface. The pressure profiles also show that there is an increased pressure drop due to PLA in the wormhole versus in a filter cake on the surface.
This paper details a new method of visualizing and analyzing the effect of PLA in a multistage acidizing treatment. Empirical correlations are presented for estimating the pressure drop caused by PLA, both as a filter cake on the formation surface and as a filling inside wormholes. The correlations were incorporated in a comprehensive carbonate acidizing model to predict the diversion efficiency of PLA particles. The simulation is verified using published field trials of diversion treatments.
In the last decade, there have been several publications describing the use of Polylactic Acid (PLA) as a diverting agent in multistage matrix acidizing treatments. The solid polyester is particularly useful as a diverting agent because it hydrolyzes in the presence of heat and water leaving no residue in the formation, negating the need for any clean-up fluids. Most of the publications thus far focus on characterizing the physical and chemical attributes of the diverter and demonstrating its effectiveness in field trials. This paper develops some general guidelines for the application of PLA diversion in multistage matrix acidizing treatments by conducting sensitivity analysis on the design parameters of three field cases.
To carry out these sensitivity analyses, an empirically derived model that describes how PLA creates a skin factor during multistage matrix acidizing treatments is incorporated in a near wellbore simulator. This simulator also tracks the fluid interfaces, models the transient reservoir and wellbore flow, and calculates the wormhole propagation rate and a number of completion skin factors. The design parameters that will be investigated include whether PLA should be sized to enter the wormhole or to bridge at the sand face, diverter concentration, specific cake resistance, the number of diverter stages, and the total volume of acid pumped. The efficiency of the diversion treatments will be compared based on the overall final skin factor and uniformity of the skin profile along the well.
This paper reveals that PLA is significantly more effective in creating a uniform skin profile if it is designed to bridge the wormhole openings rather than to enter them. It is also shown that increasing the diverter concentration or using a diverter with a higher specific cake resistance can create a more uniform skin profile but there is an inverse relationship with the overall skin factor. It is shown that using the same volume of the diverter in a few diverter stages is better than pumping all of the diverter at once, but that there is a limit where using a larger number of stages does not add any benefit. The study highlights the need to fully stimulate the high permeability zones before pumping the PLA, and finally, it suggests that the total volume of acid used should be higher when PLA diversion is used to offset the adverse effects on the overall skin factor.
Located in the Arabian gulf, the Qatari North Field is the largest non-associated gas field worldwide with estimated reserves exceeding 900 trillion cubic feet of recoverable gas, or approximately 10% of the world's known reserves. Development of this field present tough conditions for all aspects of well drilling and completion activities. Particular challenges for performing well intervention, which have driven operators and manufacturing and service companies to develop innovative strategies and systematic technology collaboration for intervening these fields in a safe and efficient manner.
Recently, two new sub-horizontal wells with multiple reservoir zones needed to be perforated and selectively stimulated. Considering safety factors and operational efficiency, the insertion and retrieval under pressure system was identified as the best alternative to convey an average length of 600ft of 2 7/8-in. guns in single trips with coiled tubing (CT). Although this system has been successfully used in other regions, downhole adverse conditions required specifc components and implementing innovative methods, including the use of 5/16-in. braided slickline for gun deployment, and 2 3/8-in. CT with fiber optic telemetry capability for accurate depth correlation, precise actuation of the firing head system and confirmation of gun detonation.
As result of a dedicated planning and preparation process, the two wells were perforated in controlled conditions and each of the applied technologies proved its value. The use of 5/16-in. braided slickline reduced the gun deployment time by at least 2 days from the planned schedule, and the H2S rated connectors and the pressure-pulse firing head gave the confidence to avoid any issues when the perforating assembly was downhole. In respect to the CT real-time telemetry system, this technology provided an exceptional indication of bottomhole conditions throughtout the operation by enabling precise control of the firing head mechanism, identification of gas/water fluid contact in the well, and monitoring of formation response, which eliminated the need for initially planned nitrogen lift operations.
This paper describes the selection process of the key technologies deployed for performing CT conveyed perforating operations in two sub-horizontal wells in Qatari North Field, and discusses the workflow developed for those interventions. It then presents case studies and lessons learned and provides conclusions from the experiences gained for performing CT conveyed perforating operations in North Field.