How much oil and gas (3650)

1. Learn the words and word combinations before reading:

at a profit – с прибылью

porosity - [pL'rO siti] - пористость, ноздреватость; скважинность

permeabil­ity - ["pWmjq'biliti] - проницаемость, проходимость

well log – промысловая геофизика, каротаж

rock matrix - ['meitriks] -материнская порода; цементирующая среда

core - колонка породы, керн

fluid saturation ["sxCq'reISqn] - насыщенность флюидом

fraction – фракция, частица

pressure ['preSq] - давление; сжатие, стискивание

drive [draiv]- передача; вытеснение (нефти из коллектора газом, водой) пластовый режим, проходить (горизонтальную выработку), штрек по простиранию пород

sealing [sJliN] fault – непроводящий сброс ант. nonsealing – проводящий

drillsteam test- апробирование пласта испытателем на скважине

drilling rate log = drilling time log – диаграмма скорости проходки скважины; механический каротаж

mud log – газовый каротаж, геохимическое и геофизическое исследование скважин по буровому раствору

tracer – изотопный индикатор

2. Read and translate the text:

When deciding whether to develop a field, a company must estimate how much oil and gas will be recovered and how easily they will be produced. Although the volume of oil and gas in place can be estimated from the volume of the reservoir, its porosity, and the amount of oil or gas in the pore spaces, only a proportion of this amount will be recovered. This proportion is the recovery factor, and is determined by various factors such as reservoir dimensions, pressure, the nature of the hydrocarbon, and the development plan.

More specifi­cally, petroleum engineers have to know:

-- the pore spaces of a rock (porosity). Porosity is the volume frac­tion of space not occupied by the rock matrix. Not only average porosity is important but also porosity distribution, both vertically and horizontally. Reser­voir porosity is determined from measurements on cores and well logs using relationships that are some­what empirical.

-- how the pore spaces are interconnected (permeabil­ity), if permeability is good and the reservoir fluids flow easily, oil, gas and water will be driven by natural depletion into the well and up to the surface.

-- the nature of the fluids filling the pore spaces (fluid saturation). Expansion of the gas cap and water drives oil towards the well bore. Gas and water occupy the space vacated by the oil. In reservoirs with insufficient natural drive energy, water or gas is injected to maintain the reservoir pressure.

-- the energy or pressure that may cause the fluids to flow (drives). Pressure is the driving force in oil and gas production. Reservoir drive is powered by the difference in pressures within the reservoir and the well, which can be thought of as a column of low surface pressure let into the highly pressured reservoir.

-- the vertical and areal distribution of reservoirs and pore-connected spaces, and

-- barriers to fluid flow (sealing and nonsealing faults, stratigraphic barriers, etc.).

These facts have to be determined from available information, which probably consists of: surface seismic, gravity, magnetic, and other geo­physical data, borehole logs of various types, cores taken in boreholes, analyses of fluids recovered in drillstem tests, production and pressure data, specialized geophysical measurements, occasionally tracer data, and drilling rate logs, mud logs, and other well data.

Well logs, geologic background, and well-to-well log correlations supplemented by seismic character stud­ies (will be seen further) give an overall picture of the stratigraphy and stratigraphic changes across the reservoir, and pro­duction and pressure data (and occasionally tracer data) give information about the connectivity of reser­voir members between wells. Surface geophysical data, while lacking the vertical resolution of borehole logs and cores, provides the only data source that gives detailed information about areal distributions.

The proportion of oil that can be recovered from a reservoir is dependent on the ease with which oil in the pore spaces can be replaced by other fluids like water or gas. Tests on reservoir rock in the laboratory indicate the fraction of the original oil in place that can be recovered. Viscous oil is difficult to displace by less viscous fluids such as water or gas as the displacing fluids tend to channel their way towards the wells, leaving a lot of oil in the reservoir.

Each oil and gas reservoir is a unique system of rocks and fluids that must be understood before production is planned. Of course all these facts are to be determined and calculated by a very synergistically working team of development geologists, geophysicists and petro­leum engineers using all the available data to develop a mathematical model of the reservoir. Computer simulations of different production techniques are tried on this reservoir engineering model to predict reservoir behaviour during production, and select the most effective method of recovery. For example, if too few production wells are drilled water may channel towards the wells, leaving large areas of the reservoir upswept.

Factors, such as construction requirements, cost inflation and future oil prices must also be considered when deciding whether to develop an oil or gas field. When a company is satisfied with the plans for development and production, they must be approved by the Government, which monitors all aspects of oil field development.

3. Explain the words:

porosity, permeabil­ity, fluid saturation, sealing and nonsealing faults, drillstem tests, stratigraphic changes across the reservoir, areal distribution.

 

4. Answer the questions:

1. How can the volume of oil and gas in place be estimated? 2. What is the reser­voir porosity determined from? 4. What gives detailed information about areal distributions? 5. What do a geologist and a geophysicist have to know about oil reservoirs?

 

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