Total Core Recovery Research Articles

Improving the Relationship Between Flow-Zone Indicators With Lithofacies

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 186005, “An Innovative Approach Toward Improving the Relationship Between Flow-Zone Indicators With Lithofacies: A Case Study in a Carbonate Oil Field in the Middle East,” by N.S. Hashim, A.F. Zakaria, and N.A. Ishak, Petronas, prepared for the 2017 SPE Reservoir Characterization and Simulation Conference and Exhibition, Abu Dhabi, 8–10 May. The paper has not been peer reviewed. The F field in the Middle East currently has more than 40 producing wells in the center of the structure. The uneven well distribution limits the understanding of 3D reservoir characterization, particularly in the flank areas. A fit-for-purpose integrated reservoir-characterization study was carried out. The exercise, outlined in the complete paper, confirms the heterogeneity within B formation (the primary oil reservoir within F field), and it captures the changes in reservoir quality laterally and vertically. Introduction F field is located in the northeastern part of the Arabian Peninsula. F field is a low-relief anticlinal structure aligned northwest/southeast, approximately 31 km long and 10 km wide. B formation consists of carbonate-ramp depositional settings, and has an average thickness of 200 m. Multiple development wells were drilled as part of its development plan, and its first oil production was achieved 3 years ago. Issues with reservoir characterization have arisen because of the uneven well distribution, especially in the flank area. Furthermore, only one conventional core with good recovery was available for Reservoir B, which makes it somewhat difficult to delineate the internal architecture of the carbonate ramp. B Formation Stratigraphic Interval B formation subreservoirs include Upper B (UB), Middle B (MB), and Lower B (LB); the MB and LB subreservoirs contain most of the hydrocarbon deposits. UB does not contain any hydrocarbons and is believed to be tight on the basis of log information. Each subreservoir was divided into sub-units (UB-1 and UB-2; MB-1, MB-2, and MB-3; and LB-1, LB-2, and LB-3) on the basis of pressure and fluid information. One conventional core was taken with a total length of 100 m and total core recovery of 97%. This conventional core covers the Middle B to Lower B subunits. Full-core analysis study was conducted on this conventional core, which includes routine geological analysis, routine core analysis (RCA), special core analysis, and digital rock analysis. Lithofacies Analysis The study identified seven lithofacies. Bioclastic Mudstone (BM). BM consists of a mostly micrite matrix. It is light gray to pale brown and is moderately bioturbated. In terms of reservoir characteristics, this lithofacies is poor, with no visible porosity. BM is usually deposited in an open marine slope. Bioclastic Wackestone (BW). As with BM, BW also consists of a micrite matrix. Carbonaceous wispy seams, solution seams, and stylolization are also common in this lithofacies. BW is characterized as tight, with no visible porosity. Its measured porosity ranges from 4 to 21%, with average porosity of only 10% and a permeability range between 0.1 and 7.6 md. BW is likely located in the shallow marine middle ramp.

Evaluation of a coal seam roof water inrush: case study in the Wangjialing coal mine, China

The Wangjialing Mine in southern Shanxi Province is seriously threatened by roof water and is infamous for a water inrush disaster that happened there in 2010. A root-cause-analysis was conducted. Three key issues, the height of the mining-induced fractured zone in formations overlying the coal seam, the water yield of aquifers overlying the coal seam, and working face water inflows before and after pretreatment of roof water-bearing aquifers, were studied based on the “three maps–two predictions” approach. According to the multi-source information composite principle, abundance zoning maps of the roof aquifer were made using the overlapping function of geographic information system (GIS) for five controlling factors: aquifer thickness, total core recovery, drilling fluid quantity, permeability, and thickness of brittle and plastic strata. Borehole-specific data from in-situ pumping tests were used to verify the water abundance results. For areas that did not meet the verification requirements, the weights of the controlling factors were calibrated by reestablishing the analytic hierarchy process judgment matrix. The total height of the fractured zone within the #2 coal seam roof was calculated using an empirical formula. An established roof crack safety zoning map was used to evaluate that aspect. A three-dimensional numerical simulation of the groundwater flow system was established based on the site conceptual model of the roof aquifer and was used to predict the working face inflows. The results indicated that the 20,518 working face of the 205 panel had the greatest abundance of water.

Practical Investigations on Use of Weighted Joint Density to Decrease the Limitations of RQD Measurements

Various techniques have been established in geotechnical engineering to determine the quality of rock drilled out from a borehole. These simple and inexpensive methods include total core recovery (TCR), solid core recovery (SCR), and rock quality designation (RQD). Among these, RQD provides a general indication of rock mass quality and is widely used as an index to evaluate rock quality by expressing the degree of fracturing in drill cores. The RQD was modified from the TCR method by Deere (1963) to indirectly measure the number of fractures and amount of softening or/and alteration in rock mass for engineering applications. Its simplicity, low cost, and reproducibility generally resulted in quick development of the RQD for a wide variety of rock engineering applications, such as tunnels, mining engineering, and large caverns. Nowadays, this method is considered as a standard method in drill core logging and forms a basic element of the most widely used rock mass classification systems, such as the rock mass rating (RMR) and Q-system (Bieniawski 1989; Barton 1995). However, a number of limitations such as dependence on borehole orientation and the selected threshold value for the minimum intact core length restrict the consistency of the measured values. Accordingly, several methods have been established to overcome these limitations, such as the corrected rock quality designation (RQDc) (Li et al. 2009), volumetric joint density (Jv) (Palmstrom 1982, 1985, 1986; Sen and Eissa 1992), cumulative core index (Sen 1990), and weighted joint density (WJD) (Palmstrom 1995, 2005). Although such new methods have been developed, the RQD is still used with the initial definition, without correction, in many geotechnical engineering applications, e.g., rock mass classification, rock mass strength, and modulus of elasticity. This paper reviews the conventional RQD measurement techniques by Deere (1963) and RQD measurements from the WJD (hereafter called RQDWJD) by Palmstrom (2005) using rock cores drilled out from directional boreholes at the Bakhtiary Dam site. In this way, the RQD values from different methods were compared, and a new modification is proposed, called RQDM-WJD.

Jet grouting for mitigation of installation disturbance

To reduce the impact of installation of horizontal jet grouting columns on surrounding ground, a new horizontal jet grouting technique termed controlled discharge horizontal jet grouting is developed. A field trial programme is conducted to verify the application of the technique technology. Field measurements of ground surface displacement and induced excess pore-water pressures are obtained during implementation of the technique. Five trial jet grout columns are installed at 2 m below the ground surface and subsequently exposed for measuring and testing. The observed vertical displacements of the ground surface range from 0·4 to 9·4 mm, with maximum excess pore-water pressures generated during the field trial varying between 3·5 and 25·6 kPa. The diameters of the exposed jet grout columns range from 1·1 to 1·4 m. Core samples extracted from the trial jet grout columns indicate that the quality of the jet-grouted soil formed is good, with total core recovery of 70–95% and rock quality designation of 79–92%. Unconfined compressive strength tests show that the 28-d strength ranges from 0·9 to 1·5 MPa, and Young's modulus at 50% failure load (E50) is between 61·5 and 145·3 MPa. The field trial results confirm the applicability of the technique for achieving low-impact installation of horizontal jet grouting.

Using borehole geophysical data as soft information in indicator kriging for coal quality estimation

Mineral resources estimation comprises basically two stages: (i) data collection, analysis and validation, and (ii) the estimate of the grades and tonnes of the deposit. The most often applied method for obtaining geological data during mineral exploration is rotary drilling with total core recovery. High drilling costs make borehole geophysical logging attractive to obtain the maximum possible information from each borehole helping to understand ore intersections, grades variability, and extension of the deposit and its continuity. In this paper, borehole geophysical logging was used to enhance the sampling survey and to derive grades indirectly (without lab analysis) with a certain amount of uncertainty. Soft indicator kriging (IK) was selected to estimate coal quality by combining hard data from drill holes and soft data from geophysical logging correlation. The method showed to be adequate to incorporate the uncertainty associated with the geophysical derived grade values. The results were compared to the conventional procedures using grades determined via core analysis and ordinary kriging. Borehole geophysical logging proved to be essential to define the features of ore deposit and soft IK provided results with acceptable precision and accuracy if compared to the model provided by ordinary kriging and hard data.

Jet grouting with a newly developed technology: The Twin-Jet method

The Twin-Jet method, a newly developed jet grouting technology for the instant solidification of soft ground, is presented. The basic principles of the Twin-Jet method are introduced and sodium silicate (water-glass) is selected as the binder to accelerate the hardening process of an admixture of grout and soil. Two case histories of the Twin-Jet Method, conducted in both a vertical (constructed in sandy soils) and a horizontal (constructed in clay soils) direction, are presented to show their effectiveness. Field construction shows that the admixture of grout and soil can be gelled within 5 to 10seconds. For the case history constructed in sandy soils, coring samples indicate that the jet grout columns are properly formed with a total core recovery of 80–100%, a rock quality designation (RQD) of 81–95% and a column diameter reaching 1.1m, while unconfined compressive strength (UCS) tests suggests that the 28-day UCS is within the range of 5.0–6.0MPa. For the case history constructed in clay soils, field cone penetration tests (CPT) suggest that the column diameter can reach 1.2m, and the UCS test results show that the 14-day UCS can reach 0.5MPa. All of these test results demonstrate the applicability of this newly developed technology in both sandy and clay soils.

Reply to discussion on ‘Measurement of total core recovery; dealing with core loss and gain’ by S. Valentine & D. Norbury Quarterly Journal of Engineering Geology and Hydrogeology , 44, 397–403

The Authors thank the Discusser for providing discussion on a matter that seems so straightforward, and therefore possibly banal, but that yet causes considerable difficulties in practice. We note that we are in agreement on all aspects except the concept of the ‘shuffling’ of the core extending to the records of Total and Solid Core Recovery (TCR and SCR) and Rock Quality Designation (RQD) presented on the borehole log; the treatment of Fracture Spacing is not mentioned in either the paper or the discussion, but this argument would extend to that index also. The Discusser cites BS5930:1999 (BSI 2010), where the definitions of these indices are given as ‘core recovered to length of core run’. We would go further and cite …

Discussion on ‘Measurement of total core recovery; dealing with core loss and gain’ by S. Valentine & D. Norbury Quarterly Journal of Engineering Geology and Hydrogeology , 44, 397–403

In drawing attention to the issue of ‘core gain’ the Authors have drawn attention to a problem that troubles many engineers when they encounter it, and no doubt, with the lack of formal consideration in the technical literature over the years, there have probably been any number of solutions attempted by logging engineers with, no doubt, varying degrees of success. The Authors’ solution (following the current practice as outlined in BS 5930 (BSI 2010), however, is at odds with the way I would wish to have us deal with this issue in one important aspect. It is stated, following the current guidance, that although the driller’s core run markers should not be moved, the core recoveries (TCR/SCR and RQD) should be …

Sedimentological study of the Szőreg-1 reservoir (Algyő field, Hungary): a combination of traditional and 3D sedimentological approaches

The paper presents a 3D sedimentological characterization of a delta plain reservoir. The analysis started with detailed core description studies focusing on the genetic interpretations of the sedimentary structures and multivariate statistical analyses, (including Q-mode cluster and R-mode factor analysis), of the sporadic grain-size distributions. These results made the depositional processes of channels, bar-crests and crevasse splays probable. By calibration of the well log responses to the cores with total core recovery, we were able to identify two types of vertical facies transitions: (1) mouth-bars and channels; (2) crevasse splays, crevasse channels and minor mouth bars. In addition, a vertical sequence of a relative thick distributary mouth bar was also recognized. Lateral extension was determined by contouring the sand content on surfaces parallel to the upper time horizon. On these surfaces, the sand content and porosity grid systems facilitated the use of an unconventional 3D geo-cellular modelling approach for both well-log-porosities and sand contents. Since vertical depositional facies were extended into the 3D, rock bodies of the most characteristic channel and mouth bar environments could be cut out from the porosity and sand content models. In this way not only their general geometry and internal characteristics, but also the basic geostatistical features (ratio of anisotropy, the direction of major and minor continuity) of their sand content and porosity were identified.

Measurement of total core recovery; dealing with core loss and gain

Abstract The measurement of total core recovery is apparently a simple measurement to make and so there is little guidance available on how to actually carry this out. As core drilling is carried out in an increasingly wide range of materials, the difficulties in recording this simple index also increase. This technical note sets down some of the procedures that need to be followed for efficient and accurate record taking.

Identification of karst features using seismic P-wave tomography and resistivity anisotropy measurements

A football stadium with a capacity of a hundred thousand spectators is under construction over a karst terrain, 10 km west of the old town of Istanbul, Turkey. A large cavity of approximately 30 m3 was detected beneath the sports field through a number of boreholes so that a geophysical survey was required to further investigate a portion of the sports field. We utilized seismic refraction tomography and dc-electrical method with rotated Wenner array to delineate zones with solution voids and cavities. Total core recovery (TCR) was 5–15% from boreholes where zones with low velocities were identified through tomographic inversion, whereas TCR values were above 60% in zones with higher velocities. Both low velocity zones in the tomographic images and increasing resistivity anisotropy with depth appear to indicate that the cavity extends toward the west and south at a depth of approximately 8 m, although the southward and westward extension changes in character.

Removal of exganic sulfur from coal by perchloroethylene extraction and ultrasonic wave : Yu, H.-M. et al. Zhongguo Kuangye Daxue Xuebao, 2002, 31, (3), 289–292. (In Chinese)

Mineral resources estimation comprises basically two stages: (i) data collection, analysis and validation, and (ii) the estimate of the grades and tonnes of the deposit. The most often applied method for obtaining geological data during mineral exploration is rotary drilling with total core recovery. High drilling costs make borehole geophysical logging attractive to obtain the maximum possible information from each borehole helping to understand ore intersections, grades variability, and extension of the deposit and its continuity. In this paper, borehole geophysical logging was used to enhance the sampling survey and to derive grades indirectly (without lab analysis) with a certain amount of uncertainty. Soft indicator kriging (IK) was selected to estimate coal quality by combining hard data from drill holes and soft data from geophysical logging correlation. The method showed to be adequate to incorporate the uncertainty associated with the geophysical derived grade values. The results were compared to the conventional procedures using grades determined via core analysis and ordinary kriging. Borehole geophysical logging proved to be essential to define the features of ore deposit and soft IK provided results with acceptable precision and accuracy if compared to the model provided by ordinary kriging and hard data.