Reservoir Characteristics

Rock formations that are typically important to oil and gas prodnction fall into three categories (1) source rock, (2) reservoir rock, and (3) cap rock. 

In conventional petrolenm and gas reservoirs, the formation of oil and/or gas is initiated in the sonrce rock and migrates to the reservoir rock, and its migration is stopped by cap rock. CBM reservoirs do not follow this pattern. Coal meets the criteria for sonrce rock since the very matrix of the 

CBM is adsorbed to the surface of the coal and the adsorption sites can store commercial quantities of gas as part of the coal matrix. This must not be confused with conventional pore-volume storage. Gas within petroleum reservoir rock as a gas and the traditional pressure/temperature/volume relationships hold. Adsorbed gas molecules do not behave as a gas (1) they do not conform to the shape of the container, (2) they do not conform to the modified ideal gas laws (i.e., PV ZnRT), and (3) they take up substantially less volume than the same mass of gas would require within a pore volume. 

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Ci2-Ci3 ether carboxylic acid with 4.5-6 mol EO and Ci2-C15 ether carboxylic acid with 9 mol EO as cosurfactant improve the use of alkyl-o-xylene-sulfonate as primary surfactant at different salinity while maintaining good oil solubilization [189]. It is possible to optimize the surfactant system in relation to the crude oil reservoir characteristics. 

Archie, GE, The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics, Transactions of the American Institute of Mining Engineers 146, 54, 1942. 

While drilling low-pressure reservoirs with nonconventional methods, it is conunon to use low-density dispersed systems, such as foam, to achieve underbalanced conditions. To choose an adequate foam formulation, not only the reservoir characteristics but also the foam properties need to be taken into account. Parameters such as stability of foam and interactions between rock-fluid and drilling fluid-formation fluid are among the properties to evaluate while designing the drilling fluid [13]. 

The state of the art in chemical oil recovery has been reviewed [1732]. More than two thirds of the original oil remains unrecovered in an oil reservoir after primary and secondary recovery methods have been exhausted. Many chemically based oil-recovery methods have been proposed and tested in the laboratory and field. Indeed, chemical oil-recovery methods offer a real challenge in view of their success in the laboratory and lack of success in the field. The problem lies in the inadequacy of laboratory experiments and the limited knowledge of reservoir characteristics. Field test performances of polymer, alkaline, and micellar flooding methods have been examined for nearly 50 field tests. The oil-recovery performance of micellar floods is the highest, followed by polymer floods. Alkaline floods have been largely unsuccessful. The reasons underlying success or failure are examined in the literature [1732]. 

Kopp A., Class H., et al. Investigations on C02 storage capacity in saline aquifers part 1. Dimentional analysis of flow processes and reservoir characteristics. 2009 International Journal of Greenhouse Gas Control 3(3) 263-276. 

Just as oil, natural gas is also categorised as conventional and unconventional. Unlike crude oil, however, natural gas deposits are normally classified according to the economic or technical approach, i.e., all occurrences that are currently extract-able under economic conditions are considered conventional, whereas the rest are termed unconventional. Conventional natural gas includes non-associated gas from gas reservoirs in which there is little or no crude oil, as well as associated gas , which is produced from oil wells the latter can exist separately from oil in the formation (free gas, also known as cap gas, as it lies above the oil), or dissolved in the crude oil (dissolved gas). Unconventional gas is the same substance as conventional natural gas, and only the reservoir characteristics are different and make it usually more difficult to produce. Unconventional gas comprises natural gas from coal (also known as coal-bed methane), tight gas, gas in aquifers and gas hydrates (see Fig. 3.17). It is important to mention in this context so-called stranded gas , a term which is applied to occurrences whose extraction would be technically feasible, but which are located in remote areas that at the moment cannot (yet) be economically developed (see Section 3.4.3.1). 

S. E. Cross, B. M. Magnusson, G. Winckle, Y. Anissimov, and M. S. Roberts. Determination of the effect of lipophilicity on the in vitro permeability and tissue reservoir characteristics of topically applied solutes in human skin layers. J. Invest. Dermatol. 120 759-764 (2003). 

Archie GE (1942) The electrical resistivity log as an aid in determining some reservoir characteristics. Trans AIME 146 54-62... 

A further difficulty that faces oil field modelers is the lack of information they have about downhole conditions and reservoir characteristics. Forward predictions about production are distressingly uncertain. It is therefore common to fit observed production data retrospectively—a procedure known as history matching—and to infer reservoir parameters, particularly permeabilities and relative permeabilities. 

In summary, reservoir characteristics establish most of the parameters that control capillary snap-off, and interfacial tensions are the only controllable snap-off parameters. The dependencies of interfacial tensions on phase behavior and surfactant structure define many of the objectives of the surfactant designer. 

The development of a rational strategy of surfactant design requires some way of estimating the dependence of phase parameters on surfactant structure and reservoir characteristics (e.g., salinity). Chapter 9, by Borchardt, describes a method for correlating phase and physical properties of mobility control surfactants with their molecular structures. 

Spiensen, S., Jones, M., Hardman, R.F.P., Leutz, W.K. and Schwartz, P.H. 1986. Reservoir characteristics of high- and low-productivity chalks from the Central North Sea. In Norwegian Petroleum Society (Editors), Habitat of Hydrocarbons on the Norwegian Continental Shelf. Graham and Trotman, London, pp. 91-110. 

Strong, G.E. Milodowski, A.E. (1987) Aspects of the diagenesis of the Sherwood Sandstones of the Wessex Basin and their influence on reservoir characteristics. In Diagenesis of Sedimentary Sequences (Ed. Marshall, J.D.), Spec. Publ. geol. Soc. London, 36, 325-337. 

Evans, R. (1995) Stratigraphy, fluid flow and reservoir characteristics of the Carboniferous of Ballycastle. Geol. Surv. Northern Ireland Tech. Rep., 95/5. 

The rocks in which large volumes of petroleum are able to accumulate are termed reservoir rocks. They require suitable porosity (typically 10-25%) and permeability (typically 1-1000mD 1 mD or milliDarcy = c.10 9m2), with reasonably sized pores and an impermeable cap rock or seal to prevent escape of petroleum over geological time periods. They must also be in place before the onset of oil generation. Sandstones often provide suitable reservoir characteristics. More than 60% of all oil occurrences are in clastic rocks, while carbonate reservoirs account for c.30%. The smaller molecules present in gases can escape through narrower pores than oil components, and seals are often slightly leaky with respect to gas. 

The number of passes required through an orifice to form a well-dispersed solution depends on the polymer concentration. The reservoir characteristics are needed for the final design of the orifice mixing system. Details of mixing of xanthan gum solutions were presented in an earlier study (7). ... 

Stimulation of a well is accomplished by increasing the flow capacity near the wellbore and allowing formation fluids to enter the wellbore more easily. When low permeability exists, when formation is damaged, or when altered native reservoir characteristics around the wellbore exist, near wellbore stimulation may be beneficial. 

Prediction of Solids Production. In the development of conventional oil and gas reservoirs, solids management strategies are used to avoid solids production by proper production practices or to control or prevent solids production, if it is unavoidable. The use of solids control methods is usually based on experience with analogous offset wells in the area where a new well is to be drilled. Offset well data can be used effectively if the geological and reservoir characteristics and the well drilling, completion, and production procedures are similar. It is often difficult or expensive to recomplete wells if a solids production problem occurs after initial completion of the well. In some cases, productivity may be negatively impacted if solids control is retroactively installed in... 

The principal reservoir characteristics and technical data on the field prior to the commencement of steam flooding were as follows depth down to the producing horizon was variable-ffom 90 to 150 m average thickness of the bed-iSO m bed porosity-28% permeability-1 Darcy oil fill-80% speciric gravity of crude oil under surface conditions-0.93 g/cmh oil viscosity-165 centipoise tar content of crude-45% formation pressure immediately prior to the commencement of steam Ireatment-from 1 to 3 kg/cm temperature from 4 to 6°C oil recovery factor during the 40 years of conventional production prior to EOR work-14% number of wells drilled into the block X of the field-52 number of separate unit areas-9 area of each unit-from 0.34 to 0.87 ha. 

Judging from the well-log data, both well 34 and 38 had the same reservoir characteristics. Nevertheless they reacted differently to steam flooding treatment. Thus, before the treatment, well 38 produced daily 9 t of water and 1 t of oil. Fifteen days after the steam flooding began the daily flow of water increased to 231 and that of oil to 3 t. After 6 months of treatment the corresponding daily yields were 31 t and 4 t. During the same time the temperature at the wellhead of well 38 increased to 47°C. 

In situ combustion makes it possible to put in production some oil fields whose reservoir characteristics have been already fully determined, which, however, cannot be exploited 1 any other method. 

Table 33 shows some data on Pavlova Gora crude oil, on the field s reservoir characteristics, and on the process of in situ combustion itself. Oil production from this reservoir began in October 1937 with an output of 6.S tons/day. Maximum average output per day was 21 tons. Thereafter the oil output kept on declining continuously, and towards the end of 1964, with 13 producing wells, it stabilized at S tons/day. 

Table 33. Reservoir characteristics of the Pavlova Gora oil field...

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