In the context of oil wells, pumping is a routine operation involving injecting fluids into the well. Pumping may either be done by rigging up to the kill wing valve on the Xmas tree or, if an intervention rig up is present pumping into the riser through a T-piece (a small section of riser with a connection on the side). Pumping is most routinely done to protect the well against scale and hydrates through the pumping of scale inhibitors and methanol. Pumping of kill weight brine may be done for the purposes of well kills and more exotic chemicals may be pumped from surface for cleaning the lower completion or stimulating the reservoir (though these types are jobs are more frequently done with coiled tubing for extra precision).
An oil well is a boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released along with the oil. A well that is designed to produce only gas may be termed a gas well.
In petroleum and natural gas extraction, a Christmas tree, or "tree", is an assembly of valves, spools, and fittings used to regulate the flow of pipes in an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well and other types of wells. It was named for its resemblance to the series of starting lights at a drag racing strip.
A well kill is the operation of placing a column of heavy fluid into a well bore in order to prevent the flow of reservoir fluids without the need for pressure control equipment at the surface. It works on the principle that the hydrostatic head of the "kill fluid" or "kill mud" will be enough to suppress the pressure of the formation fluids. Well kills may be planned in the case of advanced interventions such as workovers, or be contingency operations. The situation calling for a well kill will dictate the method taken.
Importance of knowing quantity
Work involving wells is fraught with difficulties as there is often very little information about the real time condition of the completion. This lack of knowledge also covers potential damage and even loss of well integrity. Therefore, it is essential for the operator to pay attention to the pressures as recorded and to the quantity pumped. A premature increase in pressure is sign of a potential blockage and continuing to pump risks burst pressure retaining components. Pumping more than an anticipated amount of fluid is a sign of a loss of integrity and a potential leak path somewhere. In either of these two situations, pumping must be stopped and the potential causes analysed.
Well integrity, in regard to oil wells, is defined by NORSOK D-010 as the "“Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well”. There are various facets to well integrity, including accountability/responsibility, well operating processes, well service processes, tubing/annulus integrity, tree/wellhead integrity and testing of safety systems.
Compressed volumes
It is vital to know the effective capacity of the completion being filled in order to understand what are sensible volumes. If pumping is to continue until reaching a desired pressurisation, then the compressibility of the fluid will become significant. It is therefore important to know how much the fluid will compress under pressure to know how much extra fluid is expected to be required.
As a rule of thumb in the oilfield, compression is governed by the equation: where ΔV is the change in volume, P is the pressure at surface and V is the volume of fluid unpressurised. k is a compression factor approximately 3.5×10−6 psi−1.
For example, a volume of 300 bbl is to be filled with brine and pressurised to 3000 psi at the surface. The compression is
Therefore, it is expected that 303.15 bbl are required to accomplish this task. If 3000 psi is achieved prior to this quantity being pumped, a blockage is to be suspected. If after pumping 303 bbl, pressurisation is not achieved, a leak is to be suspected.
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