File Name: coring and core analysis .zip
Koepf, E. Analytical techniques and procedures which permit accurate measurement of important physical properties and of fluid content of sidewall core samples as received in the laboratory are available.
Chap 2 Coring and Core Analysis Processes.pdf
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Abstract Core analysis provides the only direct and quantitative measurement of reservoir petrophysical properties and should provide the ground truth for integrated formation evaluation. However variable data quality, the sensitivity of results to different test methods, poor reporting standards, and the reluctance of some vendors to share experience and expertise have all contributed to basic mistakes and poor data quality.
It is easy to blame the vendors, but in too many cases, an inconsistent or inappropriate approach to the design, management and interpretation of the core analysis programme has been adopted and exacerbated by the conflicting requests of the end users. We present a core analysis management road map which is designed to increase the value from core analysis investments by enabling a more pro-active, more coherent and more consistent approach to programme design and data acquisition.
Firstly, this involves reviewing legacy data and understanding the impact of rarely-reported experimental artifacts on fundamental rock property measurements. Can data be corrected or re-interpreted or are new tests required? Secondly, a multi-disciplinary core analysis management strategy is described.
This is designed to encourage more effective engagement between stakeholders and the data acquisition laboratory through improved test and reporting specifications, pro-active test programme management, and real time quality control. Sw , …………………………………………………………………………… The reservoir engineer is responsible for oil formation volume factor B o from PVT experiments.
The petrophysicist is responsible for net N , porosity! Data input relies principally on logs, but log interpretation must be calibrated or verified by measurements on core. For example, net reservoir is normally defined by a permeability cut off and high resolution permeability data are only possible from core. Porosity interpretation e. These are measured on core. Water saturation can be determined directly by extracting water from core using Dean Stark methods or indirectly, from core-derived capillary pressure measurements.
In our experience however an unfortunate negativity over the value of core data has arisen principally due to: 1. Poor inter-laboratory data comparability due to the lack of standardisation and the sensitivity of core data to different test methods. For example, API RP 40 cites three principal methods used to determine porosity in routine core analysis yet these can give completely different results depending on the core plug shape. The lack of thought given to the programme test design by the commissioning end users including: appropriateness of specified core tests; the reliability of the data and their applicability; the lack of understanding of the practical difficulties faced by core analysis laboratories; and the constraints they must work under.
Historically inadequate reporting standards which give little real information on the provenance of test data and their interpretation. Strong market competition which has required the core analysis vendors to produce data more reliably, for less money, and with faster turnaround times.
In a multiple laboratory comparative SCAL study Maclean and BinNasser found that some core service contractors provided very poor quality data on some of the tests, and concluded that some of the laboratories do not have quality control protocols in-house and just report data acquired. McPhee and Arthur found inexplicable relative permeability data discrepancies between commercial laboratories testing exactly the same core material and fluids.
One laboratory produced residual oil saturation data that could not be reproduced by an independent lab and manipulated endpoint data to fit their expectation. Nevertheless, it is the end user the client! Too often core analysis programmes are ill-considered, badly designed, poorly supervised, and the results are only crudely integrated with other well and reservoir data.
The results, in terms of data acquired, are often unrepresentative or contradictory. It may be no surprise therefore that it remains an uphill struggle to convince management in some companies that the project benefits from the knowledge gained from core analysis.
The Elephant In the Room Idiomatically, the elephant in the room is an expression that applies to a problem or uncertainty that few want to discuss.
The following examples illustrate where small and generally unreported laboratory artifacts and measurement uncertainties have a significant impact on two key petrophysical data inputs: the Archie water saturation equation and capillary pressure measurements. The succeeding section describes a road map to maximize the value from core analysis and reduce or eliminate data redundancy through integrated project planning and real time core analysis management.
Core Data Uncertainties and Impact Archie Water Saturation Model Archie defined a fundamental set of equations which establishes the quantitative relationships between porosity! Many petrophysicists often have to rely on legacy SCAL data of varying vintage, frequently measured at ambient conditions.
SPE 3 Porosity Input In the formation factor test, porosity is often measured at stress, in conjunction with core resistivity, Ro, and is used to estimate porosity compaction factors for log calibration.
In one of the common test protocols, the sample is saturated in brine under unconfined conditions, and after resistivity stabilisation, is loaded into the test coreholder. As air is resistive and compressible it must be removed from the annulus between the plug and the sleeve, the end stems, and measurement system so the system is filled with brine prior to loading. The confining pressure is increased in small increments and pore volume expulsion and Ro recorded.
An examples is shown in Fig. The lower pressure curve below SCP mostly represents excess brine production. The higher pressure curve above SCP only represents pore volume compaction. The inflexion point of the curves indicates the pressure at which the coreholder sleeve exactly conforms to the surface of the test plug.
The volume of water expelled at this point represents the annulus volume SCV and is determined by extrapolating the higher pressure curve to 0psi. The SCV is deducted from subsequent volume measurements to calculate the true pore volume reduction. The volume-stress data are rarely reported, and many labs assume the same SCP and hence SCV for every sample irrespective of the plug shape and surface topology.
Unfortunately, the impact on the porosity measurements is significant. The example shown in Fig. The only difference is the test laboratory. Although this is not an issue for tests carried out at stressed conditions above SCP , in ambient condition F measurements brine clings to the surface of the plug after saturation. This must be removed otherwise the surface brine will provide a conduit for current flow so that the measured resistivity is too low. A film of surface brine of just 2.
Although these effects are eliminated if both F and I tests are measured at stress, petrophysicists often do not have the luxury of working with such data.
Surface brine effects are clearly evident in Fig. F apparently increases abruptly between 0 psi and psi but this is a direct result of ambient Ro being too low due to surface brine on the plug.
At psi the surface brine has been expelled by the core sleeve conforming to the plug surface. Water Saturation Grain loss from plug handling during testing can result in considerable uncertainties in the calculation of saturations from gravimetric measurements.
A loss in weight during a drainage experiment might be interpreted as a loss of water so that the calculated water saturation is much less than the true value. The grain loss error is magnified for an oil-water system as the fluid density difference is smaller. The goal of grain loss correction is to predict the fluid-filled pore volume at each stage of the handling and test procedures, and to validate these estimates, where possible, using measured data.
Unfortunately, such corrections can be subjective. The non-wetting and wetting phase saturations were determined from the injected mercury volumes and the core plug helium pore volume. Today, virtually all measurements are made with automated high pressure HPMI equipment that is capable of injection pressures of up to 55, psi. These instruments were specifically designed for pore size distribution tests on papers, catalysts porous material and ceramics, not for capillary pressure curves on core plugs.
The sample chambers penetrometers are size- limited to around 10 ml Fig. As the impact of volume errors on saturation estimated from immersion bulk volume and helium grain volume on small samples are large, most laboratories inject mercury to define the total mercury-filled pore volume.
This requires pressures in excess of around 25, psi. In certain formations HPMI appears to cause distortion of the capillary pressure vs. In the example shown on Fig. In both cases the test plugs were unconfined 3D injection. The distortion phenomena involved are not as yet clearly understood. They may be related to sample size percolation dependencies Hirsch and Thompson, , but they appear worse on samples containing clay-filled micropores which are not normally accessed by mercury at psi.
Continued higher pressure injection appears to progressively and permanently damage the pore system, which has a significant impact when the end user generates saturation-height curves from HPMI data. The HPMI data on plug chips form a separate population, and if unquestioningly applied in isolation, result in misleadingly optimistic hydrocarbon saturations.
Mercury Pc converted to equivalent air-water system at laboratory conditions. SPE 7 0. Core Analysis Management Road Map The chance to acquire new core data provides an ideal opportunity to minimize the uncertainties in key core-derived model inputs. The key questions that should be asked prior to embarking on this process are: 1. Are there areas of concern or anomalies or suspicious data in the database that need to be resolved? How closely does the core, log and test data agree for the well in question and the reservoir in general?
What core analysis tests do we actually need? Is the contractor interpretation correct? In SCAL reports the saturations reported are often laboratory interpretations of volumetric or gravimetric measurements — they are not measured data. Data interpretation can be subjective and less than rigorous. Can operators improve on the lab interpretation?
Core Analysis, Volume 64
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Ubani and Y. Adeboye and A. Ubani , Y. Adeboye , A. Oriji Published Engineering.
Discipline: Petrophysics Level: Foundation Instructors who teach this course:. John Jack B. Thomas X DR. JOHN B. JACK THOMAS has more than 45 years of diverse work experiences in which he has conducted or worked on hydrocarbon projects in most of the active petroleum-bearing basins of the world. He is recognized as an expert in reservoir characterization of conventional and unconventional reservoirs including those in tight gas, coalbed methane, all types of siliclastic and carbonate reservoirs. He has presented seminars in more than 26 nations on aspects of these topics.
Written to address the need for an updated set of recommended practices covering special core analysis and geomechanics tests, the book also provides unique insights into data quality control diagnosis and data utilization in reservoir models. The book's best practices and procedures benefit petrophysicists, geoscientists, reservoir engineers, and production engineers, who will find useful information on core data in reservoir static and dynamic models. It provides a solid understanding of the core analysis procedures and methods used by commercial laboratories, the details of lab data reporting required to create quality control tests, and the diagnostic plots and protocols that can be used to identify suspect or erroneous data. Colin McPhee is widely recognised as an industry expert in core analysis, petrophysics, geomechanics, and formation damage. Currently, Colin is Global Technical Head for Geomechanics and Rock properties for LR Senergy, advising clients on petrophysical and geomechanical aspects of field development, asset evaluation and well construction. After working as a wellsite geologist in the North Sea then a geotechnical engineer, Colin joined the Department of Petroleum Engineering in Heriot Watt University in Edinburgh in where he was responsible for technical and operational supervision of departmental research projects, involving petrophysical core analysis and fluid flow in porous media.
After coring, cores are transferred to the laboratory. Core analysis starts with the core gamma logging and whole core CT-scanning. Basic petrophysical.
Core Analysis, Volume 64
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Stiles, J. North Sea. This paper describes the use of core analysis data, both routine and special, in characterizing the Brent Group reservoirs in the U. The results of various special ore analysis tests conducted over the years indicate that coring fluid, core preservation, and laboratory procedures are important in defining relative permeability and capillary pressure. Examples are given of 1 the effect of oil-based mud filtrate on rock wettability; 2 the effect of extraction, drying, and test procedures on laboratory waterflood performance; and 3 variation of relative permeability arnong facies. Results also suggest how petrography may be used in assigning relative permeabilities by facies. Analysis of routine core data shows complexity within the Brent Group reservoirs even within relatively "uniform" sands.
Figure provides a flow chart for a typical core analysis process. The processes are summarised below: 1. Normally nowadays, core is recovered in aluminium or fibreglass liners. Previously, core was extracted from the barrel at wellsite. Following coring the core or core liners are recovered and assembled at wellsite. This aids re-assembly in the lab. Dean-Stark plugs may be taken for later analysis in the lab.