Core sampling

To gain an understanding of the composition of the reservoir rock, inter-reservoir seals and the reservoir pore system it is desirable to obtain an undisturbed and continuous reservoir core sample. Cores are also used to establish physical rock properties by direct measurements in a laboratory. They allow description of the depositional environment, sedimentary features and the diagenetic history of the sequence. 

In the pre-development stage, core samples can be used to test the compatibility of injection fluids with the formation, to predict borehole stability under various drilling conditions and to establish the probability of formation failure and sand production. 

If a conventional core has been cut, it will be retrieved from the barrel on the rig floor and crated. It is common to do a lithologic description at this stage. To avoid drying out of core samples and the escape of light hydrocarbons some sections will be immediately sealed in a coating of hot wax and foil. 

Other logs employed to determine N/G ratio include the spontaneous potential (SP) log and the microlog, which differentiate permeable from non-permeable intervals. The N/ G ratio can also be measured directly on cores if there is visible contrast between the reservoir and non-reservoir sections, or from permeability measurements on core samples, providing sample coverage is sufficient. 

Reservoir porosity can be measured directly from core samples or indirectly using logs. However as core coverage is rarely complete, logging is the most common method employed, and the results are compared against measured core porosities where core material is available. 

Formation permeability around the wellbore can be measured directly on core samples from the reservoir or from well testing (see Section 8.4), or indirectly (estimated) from logs. 

For direct measurement from core samples, the samples are mounted in a holder and gas is flowed through the core. The pressure drop across the core and the flowrate are measured. Providing the gas viscosity (ji) and sample dimensions are known the permeability can be calculated using the Darcy equation shown below. 

Permeabilities measured on small core samples, whilst accurate, are not necessarily representative of the reservoir. Averaging a number of samples can allow comparisons with well test permeabilities to be made. 

By taking sections from a sediment core sample of 120 cm in depth it was found that the current phthalate level is only 15% of what it had been in 1972—1978. This is despite the fact that the total usage of plasticizers has continued to increase annually. 

Natural Deposits. Natural deposits, eg, minerals and fossil fuels, are located by drilling operations. An auger, eg, a screw or worm, is turned in the earth and pulled out, and material is scraped from the auger for analysis. Alternatively, samples can be taken by hoUow core drills which, when withdrawn, enclose a core of the earth that is representative of the strata through which the drill has passed. Such core samples are used in geological surveys for fossil fuels. As the drill drives deeper into the strata, each core is extracted and placed in a shallow box and coded so that a complete cross section of the geological strata can be reconstmcted. From this, the relative thickness of coal and mineral seams can be directly measured. 

Periodic samples should he taken to assess the extent of completion of the hioconversion process. Core samples should he taken annually to monitor the movement of leached wastes in the underlying strata. 

Kem-obst, n. stone fruit, pip fruit. -31, n. kernel oil, specif, palm kernel oil Founding) core oil. -physik, /. nuclear physics, -polymeric, /. nuclear polymerism. -probe, /. core sample, -pulver, n. progressive burning powder, -pimkt, m. nucleus essential point, -riicldeinen, n. Metal.) core refining, -saft, m. Biol.) nuclear fluid, -salz, n. rock salt. 

A full bed-depth, core sample should be taken of ion-exchange resin and checked for cracked and broken beads, iron fouling, and loss of capacity. The bed should be checked for loss of volume. 

Accumulation of metals in the core sampled in the northern Lagoon, relative to the industrial core, are about 5 times lower for mercury and comparable for the other two metals. Metals reaching this area of the Lagoon are carried by fresh water streams from the basin. A very high number of small productions, whose environmental impact has not yet been adequately evaluated, contribute to this pollution. 

Hydrocarbons. In other publications the historical trend of organic pollutant concentrations, namely polychlorinated biphenys (PCBs), chlorinated pesticides DDT and metabolites DDE, DDD, and polycyclic aromatic hydrocarbons (PAHs), have been reconstructed. For this purpose the sediments of the core sampled in the Lagoon area close to the industrial district were employed (16,17). 

Neftel, A., Oeschger, H., Schwander, J., Stauffer, B. and Zumbrunn, R. (1982). Ice core sample measurements give atmospheric CO2 content during the past 40,000 yr. Nature 295,220-223. 

Rain samples collected from around the Great Lakes contained both a- and P-endosulfan (Strachan and Huneault 1979). Mean concentrations of a-endosulfan in rain samples from the Great Lakes ranged from 0.1 ng/L (n=13) to 3.8 ng/L (n=16). Mean concentrations of P-endosulfan in rain samples ranged from 1 (n=14) to 12 ng/L (n=16). The endosulfans were not found to any significant extent in snow-core samples (Strachan and Huneault 1979). Detection limits were not reported. 

Much research on the Hishikari deposits has been carried out since the discovery of gold veins in 1981. Urashima and Izawa (1983) reported fluid inclusion studies using core samples. Abe et al. (1986) made a detailed description of the veins. The regional geology of this district is described in MMAJ and SMM (1987) and Urashima et al. (1987). 

Figure 1.137. The variations of major element contents in andesite (drilling core. 8-MAHAK-4 and underground samples) away from the vein system (Shikazano et al., 2002), Diamond Hishikari Lower Andesitic tuff (underground samples) square Hishikari Lower Andesitic tuff (drilling core samples) triangle Hishikari Lower Andesitic lava (drilling core samples) x relatively fresh Hishikari Lower Andesitic lava (drilling core samples). (A) SiO content variation. (B) K2O content variation. (C) CaO content variation.

Laboratory experiments have indicated that carbonate precipitation can alter the permeability of the core samples under reservoir conditions. The precipitation reduces the gas permeability in favor of the liquid permeability. This indicates that precipitation occurs preferentially in the larger pores. 

In Table 7, a comparison of actual measurements, and also two well-known pedo-transfer functions, can be found by depth. It is important to note that there is a large difference in water content between the disturbed soil core samples and the undisturbed samples. Additionally, the two pedo-transfer functions also exhibit a large difference in predicted water content. Therefore, when doing calculations or trying... 

S. Anferova, V. Anferov, D. G. Rata, B. Bliimich, J. Arnold, C. Clauser, P. Blunder, H. Raich 2004, (A mobile NMR device for measurements of porosity and pore size distribution of drilled core samples), Concepts Magn. Reson. Part B 23B (1), 26-32. 

High pressure equipment has been designed to measure foam mobilities in porous rocks. Simultaneous flow of dense C02 and surfactant solution was established in core samples. The experimental condition of dense CO2 was above critical pressure but below critical temperature. Steady-state CC -foam mobility measurements were carried out with three core samples. Rock Creek sandstone was initially used to measure CO2-foam mobility. Thereafter, extensive further studies have been made with Baker dolomite and Berea sandstone to study the effect of rock permeability. 

The slopes of the peaks in the dynamic adsorption experiment is influenced by dispersion. The 1% acidified brine and the surfactant (dissolved in that brine) are miscible. Use of a core sample that is much longer than its diameter is intended to minimize the relative length of the transition zone produced by dispersion because excessive dispersion would make it more difficult to measure peak parameters accurately. Also, the underlying assumption of a simple theory is that adsorption occurs instantly on contact with the rock. The fraction that is classified as "permanent" in the above calculation depends on the flow rate of the experiment. It is the fraction that is not desorbed in the time available. The rest of the adsorption occurs reversibly and equilibrium is effectively maintained with the surfactant in the solution which is in contact with the pore walls. The inlet flow rate is the same as the outlet rate, since the brine and the surfactant are incompressible. Therefore, it can be clearly seen that the dynamic adsorption depends on the concentration, the flow rate, and the rock. The two parameters... 

At higher Q, however, where the static structure factor reveals the asymptotic power law behavior S (Q, 0) Q 1/v, the assumption of ideal conformation clearly fails. In particular, this is evident for the core (sample 1) and shell contrast conditions (sample 2). 

Other potential monitors of historical trace elements are core samples of ice, peat, and lacustrine deposits. Each individual stratus reflects the environment in which it formed. Analyses of these core samples could reconstruct the past local and regional environmental history. 

---