Diamond Coring Research Articles

Development of Multi-stage High Matrix Diamond Coring Bit

An important way to improve overall drilling efficiency is to crease each bit's life and footage,, high matrix diamond coring bits are especially used in deep hole. In this paper, the brazing process of designing and manufacturing high matrix diamond coring bit was introduced. Firstly, impregnated diamond blocks were manufactured using hot pressing method; secondly, new drill bit steel body including waterway was processed; in the end, the impregnated diamond blocks was welded on the new drill bit steel body using brazing process. Using brazing process, a φ75/54.5 two-stage high matrix diamond coring bit was developed, its work layer is 15mm, the experimental results showed that the drilling efficiency increased, and the bit life improved over 50% comparing with the conventional impregnated diamond coring bit. And then, a φ75/54.5 three-stage high matrix diamond coring bit was developed, its work layer is 22mm, and the bit life improved over 120%.

Recognition of drilling-induced remanent magnetization by Q-factor analysis: a case study from the KTB-drillholes

Drilling-induced magnetizations (DIRM) have been detected in the rocks of the KTB (German Continental Deep Drilling Program) by determining the Königsberger factor ( Q-factor), the ratio of remanent to induced magnetization. Specimens from the outer part of the drillcores show significantly enhanced Q-factors (up to 10 times) compared to those from the internal part. Contamination by coating with abrasive material, for example from the drill bit, and grain size variations due to cutting action of the diamond coring system, can be excluded. The DIRM is interpreted to be caused by the magnetization of the core barrel and drill string, which produce higher fields close to rim than in the interior of the drill core. After removing the DIRM contaminated samples from the database, the Q-factors for the main KTB rock units have mean values of 4.8 for the gneiss units and 1.6 for the metabasite units. The uncontaminated data set fits in the appropriated field of the susceptibility— Q plot of Henkel [J. Appl. Geophys. 32 (1994) 43–53] for metamorphic continental rocks.

The mechanics of diamond core drilling of rocks

A series of 36 laboratory drilling tests were conducted to study the mechanics of diamond coring in rocks. The drillability of a surface-set drill bit was assessed based on the penetration rate, applied torque, and specific kerfing energy. Factors governing efficiency of the diamond core drilling included wight-on-bit, core bit rotational speed, and rock types. Results of the experiment indicated that penetration rate and applied torque of the drilling increased exponentially as the weight-on-bit increased. However, the specific kerfing energy decreased as the weight-on-bit increased. The effect of rotational speed of the bit on the penetration rate was found to be significant. An exponential relationship between the penetration rates and the uniaxial compressive strengths of rock samples was noted.

New downhole tools improve core recovery : D. P. Huey & M. A. Storms, Oil & Gas Journal, 93(4), 1995, pp 42–47

The need to analyze cores at downhole conditions prompted the development of a series of pressure core barrels, which can capture cores without disturbing the sample through depressurization. In upper marine sediments, tungsten carbide insert roller cone bits tend to have life expectancies of several hundred rotating hours and thousands of meters of penetration. A bit can drill through hundreds of 10-m core intervals before a pipe trip is required for a bit change. For time efficiency in coring operations in water depths averaging 3,000--5,000 m, both the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) made a full commitment to wire line coring techniques wherever possible, thereby minimizing the number of pipe trips. The initial rotary core barrel became inadequate for the high quality of cores desired for scientific analysis. The first new core barrel developed by DSDP to satisfy the increased scientific specifications was a wire line-retrievable pressure core barrel. The paper describes this pressure core barrel, as well as a pressure core sampler, hydraulic piston corer, advanced piston corer, extended core barrel, motor-driven core barrel, core catchers, coring mud motor, and a diamond coring system.

Drilling-Induced Fractures in Borehole Walls

Summary Drilling-induced fractures in borehole walls are investigated by ring tests, flow tests, and microscopic studies. Each drilling method producescharacteristic fracture patterns in the hole wall. Weaker rock drilled withlarge drill bits shows more intense damage than stronger rock drilled withsmall bits. The fracture zones, usually less than 5% of the hole radius, havean insignificant effect on the rock permeability around borehole plugs. Introduction Knowledge of the hydrological and mechanical characteristics of rock nearboreholes is important for (1) determining the deformation and stability of aborehole; (2) calculating fluid flow into, out of, or parallel to holes; (3)evaluating the seating performance and axial strength of borehole plugs andperformance and axial strength of borehole plugs and of casing cement; and (4)determining any mechanical interactions at the borehole wall. Rock adjacent toa deep borehole usually is damaged by (1) the drill bit, (2) stress relief ofthe rock, (3) pressure and invasion of the drilling fluid, and (4) the scouringaction of rock fragments brought up from the bottom under high velocity andpressure. The complex influence of these factors makes analysis of the behaviorof the rock around boreholes difficult. Borehole instability can take severalforms. Hole size can he reduced when plastic or time-dependent flow squeezesrock plastic or time-dependent flow squeezes rock into the hole. Holeenlargement can he caused by caving of shales or by hard-rock spalling. Identification and analysis of potential instabilities require informationpotential instabilities require information about the conditions of the rockaround the borehole immediately after drilling. Borehole wall fractures inducedby drilling may be small. However, the rock around deep boreholes usually issubjected to a high stress gradient with the maximum tangential stress near theborehole wall. Deformation and failure of a borehole are therefore affected bythe presence of the damaged zone. The presence of a damaged zone also mayexplain why the tangential compressive stress required to induce boreholebreakouts is higher than the compressive strength of the rock obtained fromuniaxial and triaxial compression tests. For borehole sealing or cementing, microfractures induced by drilling could increase the annular zone permeabilityand thereby reduce the ability to permeability and thereby reduce the abilityto seal it. The microfractures could reduce the stiffness of the rock aroundthe borehole plug and may lead to a reduction of the mechanical interaction atthe plug/rock interface and a decrease of the axial strength of the plugs. Theobjective of the research reported here is to identity characteristics ofdrilling-induced fractures in the walls of different sized holes drilled bythree methods. This investigation concentrates on the influence of theinteraction between drill bit and rock, isolated from other factors likely tobe present in deep-hole drilling, such as stress present in deep-hole drilling, such as stress relief, high pressure and velocity of drilling fluids, and highthermal gradients. This approach allows a detailed investigation of suchparameters as bit type, bit size, energy input, and Petrographical andmechanical properties of the rock. properties of the rock. Methods of Investigation The experimental assessment determines the fractures in hole walls producedby diamond coring, percussion, and rotary drilling at low confining pressure. Hole diameters range from 38 to 102mm. Three main lines of investigation areused:an indirect damage investigation by identifying the change in tensilestrengths of the rock directly around the borehole walls by means of tensiontests,investigation of damage-zone permeability by flow testing, andavisual permeability by flow testing, anda visual inspection of damage bypetrographic microscopy and scanning electron microscopy (SEM). The rockstested are Pomona basalt (0.5 × 0.5 mm grain size) and Grande basaltic andesite(0.1 × 0.1 mm). Drilling in the field and in the laboratory is performed at lowconfining pressures. Table 1 summarizes drilling parameters. Fuenkajorn and Daemen described detailed drilling specifications and procedures. Making thesedrilling simplifications dramatically simplifies the experimental proceduresand allows the development of a much broader data base. Concerns about thesimplifications are valid and recognized, yet valuable information can begained from simplified tests. Ring Tension Tests The ring tension test measures the tensile strength of rock disks with acenter hole. Therefore, the strength and deformation results should besensitive to the condition of the borehole wall rock, which may have beenaltered by drilling. February 1992 JPT P. 210

Cutting Technique and System for Biological Shield

The decommissioning program of the Japan Power Demonstration Reactor (JPDR) is under way. For the purpose of dismantling the biological shield of the JPDR, a diamond sawing and coring technique and an abrasive-water jet cutting technique have been developed. In the technical development, the influence of various factors on the cutting performance and the characteristics of secondary products were investigated. As a result, remote cutting systems that incorporated these techniques were fabricated for the dismantlement of the highly activated region of the biological shield.

Scottish vitrified forts: TL results from six study sites

Abstract The background and potential of Scottish vitrified forts for TL dating were outlined at the last Specialist Seminar together with a dosimetric survey and feasibility study based on destratified samples from museum collections. It was concluded that the material was worthwhile, both from the archaeological point of view, and for the opportunity to work on large, synchronously fired samples with geologically monogenetic minerals. Six sites were selected for more detailed study and samples extracted from infinite gamma matrices using a diamond coring technique. Problems were encountered when attempting to apply the quartz inclusion technique, due mainly to severe supralinearity of the dose response of the high temperature TL signals. Evidence for competition between high temperature and low temperature TL peaks was obtained, which invalidates the use of ambient laboratory irradiation to construct meaningful dose-response curves. Feldspar inclusion techniques were therefore used to obtain TL dates from the sites of Finavon (Angus), Tap O'Noth (Grampian), Craig Phadrig (Inverness), Knockfarrel (Dingwall), Langwell Dun (Strathoykel) and Dun Lagaidh (Loch Broom). The results range from the late 3rd millenium BC to the late 1st millenium AD, extending the timespan over which vitrified forts occur, and suggesting that these monuments cannot be ascribed to a single archaeological period. TL dating therefore appears to be well suited to establishing the relationship between site morphology and chronology for this class of monuments.

Scottish vitrified forts: Background and potential for TL dating

Scottish vitrified forts have been the subject of considerable interest since their discovery in the late 18th century. This presentation deals with the nature of these sites, their archaeological, historical and technical backgrounds, the existing chronological evidence from 14C dates and the potential for thermoluminescence dating revealed by a short feasibility study. The dosimetric properties of a range of sites are evaluated in some detail using a combination of X-ray fluorescence analysis, neutron activation analysis, high resolution gamma ray spectrometry and on site NaI spectroscopy. Favourable conditions are encountered in many cases particularly for samples extracted from infinite gamma matrices using a diamond coring technique. The TL properties of quartz inclusions from such samples are discussed. In addition to examples showing conventional behaviour, some samples have exhibited severe supralinearity coupled to sensitisation which presents obstacles to dating. Tests for such “malign” behaviour are proposed which will add to the reliability of TL dates from this type of sample.

Application of Computer Technology to Reservoir Studies in Canada

Abstract Three-dimensional block models of petroleum reservoirs can be mathematicallyconstructed and solved by high-speed digital computers. Machine programs havebeen written which will solve a reservoir model consisting of more than 5,000 blocks. This permits the effect of areal variations of thickness, porosity and permeability to be studied in much more detail than was formerly possible. Themodels are particularly applicable in pressure maintenance and secondary recovery studies, but are also useful for optimizing well spacing during development operations. Introduction In the oil-producing areas of Canada, the use of mathematical model studies performed by high-speed computers is feasible for more major fields and wouldproduce more advantageous information than in any comparable oil-producing areaof the world today. This is primarily because the Canadian oil industry is ayoung one; most fields have been developed since the importance of applyingreservoir engineering principles to production was realized. Also, thedevelopment has taken place during a period when advanced technology permitted the acquisition of adequate data on reservoir and formation characteristics.That is, diamond coring and methods of regular and special core analysis were available, and modern logging methods, with logs which would give quantitative information, were offered. During the major development period, members of both industry and the Conservation Board recognized the need for obtaining sufficient reservoir data, not only from cores and logs but also from performance, so that well production tests, pressure surveys and build-up or drawdown data are usually available. Also, the importance of early pressure maintenance projects to obtain maximum recovery, and cooperation in the unitization of fields to obtain this end, has been well recognized. Maximum use of the available data for reservoir performance studies and predictions can be made today through numerical models designed for modern computers. We have used these models successfully in a number of large fields, and their value has been proved.

Whole-Core Analysis Methods and Interpretation of Data from Carbonate Reservoirs

Introduction During recent years reservoirs where the hydrocarbon storage capacity and the permeability characteristics are due chiefly to fractures and vugs, and tight formations with non-homogeneous porosity development, have become of major importance in West Texas oil production. Diamond coring equipment and methods were devised which permitted excellent recovery of cores from these formations. Examination of these cores with erratic porosity development frequently indicated individual fracture or vug volume greater than the "perm-plug" sample normally used in conventional analysis. It is evident that actual reservoir properties are more closely approached in the sample as the sample size is increased and that the entire core from this type of formation should be analyzed. Although the literature on general whole-core analysis procedures has been rather limited many innovations have been introduced, both in methods of analysis and in the interpretation and application of the data. The experienced core analyst has determined a set of optimum conditions which permit a confident approach to his specialized work. These optimum conditions include a completely cored interval, beginning several feet above the pay zone, cut with large diameter coring equipment at maximum speed in a properly selected drilling fluid, pulled to the derrick floor in minimum time, described and logged by an experienced man, properly preserved by quick-freezing in dry ice or by sealing in plastic or other suitable means, and delivered immediately to a well-equipped laboratory where the tests are made on maximum-sized samples. Current coring equipment and practices permit a close approach to these optimum conditions. Coring and Sampling of Core Although the successful application of the diamond bit was a great step forward in the coring of dense carbonate reservoirs, there still is no means available to recover a sample of the reservoir in an undisturbed condition. Normally, the drilling mud filtrate flushes the core to an irreducible oil saturation. As the core is brought to the surface, the gas in solution in this residual oil is evolved, expands and expels oil and water until liquid saturations are reduced to the point where only gas will flow. The core, as recovered at the surface, then, contains residual oil after water flushing and solution gas drive, some original water and some mud filtrate, and solution gas from the oil. There appears to be a relationship between the formation volume factor of the oil and the efficiency of liquid expulsion by the gas as it expands with pressure reduction.

Analysis of Fractured Limestone Cores

Abstract A method is outlined for the analysis of large cores, developed primarily forthe purpose of obtaining reliable data on fractured or vugularlimestones. Porosity and fluid saturations are determined by a modified Dean-Starkextraction after initially bringing the samples to 100 per cent liquidsaturation by a vacuum-pressure method. Horizontal permeabilities on the wholesamples are determined in two directions, parallel and perpendicular to thedirection of principal fracturing. Results are presented for various types of formations. A comparison is madebetween data obtained by this special method and the method of conventionalanalysis, and discussion is given of the relative advantages and limitations ofeach. In view of this comparison a modified method for the analysis offractured and vugular formations is proposed, which method retains theadvantages of the previously outlined techniques but gives promise of speedingup the analysis. Introduction For many years the greater part of the production in the Permian Basin was fromformations of Permian and Pennsylvanian age. While production from theseformations is still the predominant production, deeper prospecting has broughtto light older formations with oil productive characteristics. Attempts to corethese deeper horizons were at first usually characterized by poor recovery. Theold rule of thumb, "good core recovery - poor well" was originated andremained in effect until recently. With the advent of diamond coring and theincreased efficiency in drilling and coring operations, the old adage has lostits significance. Formations of Devonian, Silurian and Ordovician ages weresuccessfully cored with varying degrees of recovery. The cores thus obtainedwere surprising and in some cases disappointing. Good recovery from theseformations led to speculation as to the feasibility of analysis and the meaningof data obtained from conventional analysis. Commercial laboratories wereengaged to analyze these cores, and their results indicated that data obtainedby conventional methods would be of little value. From visual inspection it wasapparent that in many cases the effective porosity for storage of hydrocarbons, and permeability, were contained largely in fractures and solution cavitiesrather than in the primary crystalline structure of the formation. In othercases the solution cavities augmented the effective porosity of the primarycrystalline structure, or fractures enhanced the permeability of the latter sothat the formation might respond favorably to acidization and becomecommercially productive. Since the spacing of the cavities and fractures wasoften comparable to the core diameter, it was evident that the entire coreshould be analyzed instead of small fragments. T.P. 2913

Core Analysis of Fractured Dolomite in the Permian Basin

Abstract Evaluation of Ellenburger reservoirs in West Texas has beep an uncertainmatter at best because of the lack of cores and suitable core-analysis method.Large amounts of oil are produced from sections from which sample cuttings areobtained that contain little porosity and no oil saturation. It has long beenrealized that the formation in some areas contained numerous fractures andsolution cavities that probably contained the major part of the oil present butthe magnitude of the porous system containing oil has been unknown. Diamond coring equipment, used in the mining industry for many years, hasbeen developed for oil-field use to obtain high core recovery in fractureddolomite that is not possible with conventional coring equipment. A 36-ft section of the core recovered from a fractured Ellenburger reservoirwas analyzed by a unique but simple method to obtain the first definiteevaluation of one section of the producing formation. The cores and the methodof analysis used are described and the results are discussed in somedetail. Discussion The first successful known analyses of cores recovered from the Ellenburgerformation in the Permian Basin area were made on cores recovered with the useof diamond core heads. Conventional coring methods previously used have had lowcore recovery and standard methods of analysis have proved to be inadequate forevaluation of those cores that were recovered. Core Description The Ellenburger formation to be discussed was cored using diamond core headsand oil-base drilling fluid. Of the total 103 ft cored to a depth of 8893 ft inthe Ellenburger, 99 ft or 96 pct was recovered. The dolomite cores were described as gray to white, crystalline to coarselycrystalline, with chert and calcite inclusions. Occasional shale partings 1/8to 1/4 in. in width were noted. A small amount of green clay was found in someof the coarsely crystalline material. No intergranular porosity was found byinspection in any of the cores. The core was highly fractured over most of its length with not more than twocontinuous feet that failed to contain fractures. The fractures were nearlyvertical and varied in width from those barely visible to as much as onemillimeter. T.P. 2432

Diamond Coring in the Rangely Field, Colorado

Abstract This paper presents the development of diamond coring of the Weber sand sectionin the Rangely Field, Colorado. The description and operation of thediamond-coring equipment is included as well as the economics and resultsobtained by its use. Diamond coring is compared with the other methods used fordrilling the Weber sand. Two types of diamond coring are discussed. The firstand the one used most extensively is the regular 6 1/8 X 3 ?:-in. diamond bitand bottom hole 50'Ft barrel. The second type, which has also been usedsuccessfully by Stanolind, consists of a 4 13/16 X 2 11/32 in. cutting bit andreverse circulation coring equipment. The first type will be referred to asregular or conventional diamond coring while the latter type will be referredto as reverse circulation diamond coring. Introduction Diamond coring has been used for many years in mines, quarries, surface coringat dam sites, laboratory work, and so on, but, until recently, had never beenused very extensively in coring oil sands and other oil-bearing strata. It wasdemonstrated early in its development that hard formations could be cut rapidlyand that core recoveries far exceeded those obtained with conventional hardrock bits and quite often 100 pct recovery was obtained. However, the poorlyconstructed diamond-coring equipment and resulting high costs of early diamondcoring slowed down its progress. Early in the development of the Rangely Weber field, Rio Blanco County, Colorado, the Rangely Engineering Committee selected key wells that were tocore the Weber section in its entirety. These cores were to be analyzed andvarious sections tested to gather sufficient information so that accuratereservoir studies could be made. The number of wells selected were kept at aminimum inasmuch as the productive Weber section, which is found at anapproximate depth of 6000'Ft, is thick, being as much as 600 to 700'Ft on topof the structure. The Weber section is also comparatively hard to drill. Forinstance, one well took 60 days to core 490'Ft of Weber sand with conventionalcoring equipment. It was noticed, however, that Core Laboratories diamond plugcutter could quickly cut a plug from one of these hard cores. This fact led tothe serious consideration of diamond coring the Weber sand. The first diamond coring at Rangely was performed by Stanolind in August 1946and, although we experienced some difficulties, the results definitelyindicated that diamond coring would be successful at Rangely for coring theWeber sand. As more wells were cored and the equipment improved somewhat, diamond coring became less expensive than drilling the Weber sand with theconventional rock bit. In less than one year diamond coring has definitelyproved its usefulness in oil-field drilling operations in the Rocky Mountainarea where formations quite often drill very hard. The practice of spot coringin hard oil-bearing formations with conventional coring equipment is giving wayto diamond coring of the entire sections, thus giving an operator the completepicture. T.P. 2301