Wells – Receptacles – With separate air chamber having openable passage
Patent
1994-11-04
1997-03-11
Dang, Hoang C.
Wells
Receptacles
With separate air chamber having openable passage
166169, 166264, E21B 4908
Patent
active
056092059
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a well fluid sampling tool and to a well fluid sampling method.
Hydrocarbon fluids (oil and gas) are found in geological reservoirs wherein they are contained at a high pressure (relative to ambient atmospheric pressure), and usually also at an elevated temperature (relevant to ambient atmospheric temperature). At such pressures, the gas is dissolved in the oil such that the reservoir fluid initially exists as a single-phase fluid, but the reservoir fluid will release dissolved gas to form a two-phase fluid with separate gas and oil components if the reservoir fluid has its initial pressure sufficiently reduced towards ambient atmospheric pressure. Also, the initial relatively high temperature of the reservoir fluid results in volumetric contraction of a given mass of fluid as it cools toward ambient atmospheric temperature if withdrawn from the well.
When hydrocarbon exploration wells are drilled and hydrocarbon fluids are found, a well fluid test is usually performed. This test usually involves flowing the well fluid to surface, mutually separating the oil and the gas in a separator, separately measuring the oil and gas flow rates, and then flaring the products.
It is also desirable to take samples of the oil and gas for chemical and physical analysis. Such samples of reservoir fluid are collected as early as possible in the life of a reservoir, and are analyzed in specialist laboratories. The information which this provides is vital in the planning and development of hydrocarbon fields and for assessing their viability and monitoring their performance.
Reservoir fluids and gassee can have a complex composition and often include compounds such as hydrogen sulphide (H.sub.2 S), carbon dioxide and other trace elements including mercury which, when produced, can have a significant effect on process design, product sales and the environment.
During well testing of newly discovered reservoirs, it is essential that the oil company gains an accurate understanding of the fluid composition in order properly to evaluate the downstream potential of the reservoir. Flow periods are normally kept short during well testing because of the very high cost of the operation.
During a typical flow period of 18 to 24 hours, low levels of H.sub.2 S may not be detected at a surface analytical station because of chemical reaction of the H.sub.2 S with metallic tubing in the well completion between reservoir and surface, such that the H.sub.2 S is effectively sequestered before it reaches the analytical station. (Such chemical reaction tending to conceal the presence of H.sub.2 S in reservoir fluids will tend to be accelerated at the elevated temperatures and pressures commonly prevailing during well testing.) Current practice, when low H.sub.2 S levels are detected, is to flow the well for an extended period (sometimes several days) until fluid component levels stahllisa at the surface analytical station. This extended flow testing is very costly and nevertheless there is still uncertainty about the true levels of H.sub.2 S in the reservoir.
There are two ways of collecting reservoir samples:
In Bottom Hole Sampling (BHS) a special sampling tool is run into the well to trap a sample of the reservoir fluid present in the well bore. Provided the well pressure at the sampling depth is above the "Bubble Point Pressure" of the reservoir fluid, all the gas will be dissolved in the oil, and the sample will be a single-phase fluid representative of the reservoir fluid, ie an aliquot.
Surface Recombination Sampling (SRS) involves collecting separate oil and gas samples from the surface production facility (eg from the gas/oil separator). These samples are recombined in the correct proportions at the analytical laboratory to Create a composite fluid which is intended to be representative of the reservoir fluid, ie a re-formed aliquot.
Several BHS tools are currently available commercially, which function by a common principle of operation.
A typical BHS tool is run into the well to trap a sample of reservoir flui
REFERENCES:
patent: 3095930 (1963-07-01), Kisling, III
patent: 4291585 (1981-09-01), Kolb et al.
patent: 4717473 (1988-01-01), Burge et al.
patent: 5058674 (1991-10-01), Schultz et al.
Brown Jonathan W.
Massie Keith J.
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