Well completions

Oil well - completed Oil bearing reservoir - not completed + In combination with well symbol e.g. 

Drawdown and build-up surveys are typically performed once a production well has been completed, to establish the reservoir property of permeability (k), the well completion efficiency as denoted by its skin factor (S), and the well productivity index (PI). Unless the routine production tests indicate some unexpected change in the well s productivity, only SBHP surveys may be run, say once a year. A full drawdown and build-up survey would be run to establish the cause of unexplained changes in the well s productivity. 

The figure on the right shows the well with a simple well completion including a production tubing with packer, a series of surface safety valves called a Christmas tree, a subsurface safety valve (SSSV), a circulating sleeve, and a series of perforations through the casing. 

The purpose of the well completion is to provide a safe conduit for fluid flow from the reservoir to the flowline. The perforations in the casing are typically achieved by running a perforating gun into the well on electrical wireline. The gun is loaded with a charge which, when detonated, fires a high velocity jet through the casing and on into the formation for a distance of around 15-30 cm. In this way communication between the wellbore and the reservoir is established. Wells are commonly perforated after the completion has been installed and pressure tested. 

Well completions are usually tailored to individual wells, and many variations exist. The following diagrams show a completion with a gravel pack, designed to exclude sand production downhole, and a dual completion, designed to allow controlled production from two separate reservoirs. 

Whether on land or offshore, the principle of satellite development is the same. A new field is accessed with wells, and an export link is installed to the existing (host) facility. Development is not always easier on land, as environmental restrictions mean that some onshore fields have to be developed using directional drilling techniques (originally associated with offshore developments). A vertical well can be drilled offshore away from the host facility, and the well completed using a subsea wellhead. 

The worldwide annual level of drilling, as represented by well completions, exceeded 47,000 to 53,000 wells per year from 1988 through 1990 (1). During this period, the annual number of well completions for gas was approximately 11,000 wells approximately 22,000 wells were completed each year for oil. Of those wells completed for gas, 95% were ia North America. 

FIG. 25-78 Schematic diagram of an industrial-waste injection well completed in competent sandstone. (From Vreeman, H M, Standard Handbook of Hazardous Waste Treatment and Disposal, McGraw-Hill, 1988.)... 

During well completion it is sometimes desirable or necessary to treat or stimulate the producing zone to improve permeability of the rock and to increase the flow of oil or gas into the casing. This may be accomplished by use of acid or by injection of fluid and sand under high pressure to fracture the rock. Such a trcatniciit usually improves the ability of the rock to allow fluid to flow through it into the well bore. At this point the drilling and completion phases have ended. 

Oil well completed in Italy kerosine from the oil later used for lighting First distillation of gas from coal. 

Temperature logs can be taken as wells are drilled and the temperature gradient determined for the particular region. These temperature logs taken at depth are used to determine the types of drilling fluids used as drilling progresses. Also, the temperatures at depth will determine the cements u.sed in well completion operations. 

The fluid pressure in the rock at the bottom of a well is commonly defined as pore pressure (also called formation pressure, or reservoir pressure). Depending on the maturity of the sedimentary basin, the pore pressure will reflect geologic column overburden that may include a portion of the rock particle weight (i.e., immature basins), or a simple hydrostatic column of fluid (i.e., mature basins). The pore pressure and therefore its gradient can be obtained from well log data as wells are drilled. These pore pressure data are fundamental for the solution of engineering problems in drilling, well completions, production, and reservoir engineering. 

Petroleum engineers are traditionally involved in activities known in the oil industry as the front end of the petroleum fuel cycle (petroleum is either liquid or gaseous hydrocarbons derived from natural deposits—reservoirs—in the earth). These front end activities are namely exploration (locating and proving out the new geological provinces with petroleum reservoirs that may be exploited in the future), and development (the systematic drilling, well completion, and production of economically producible reservoirs). Once the raw petroleum fluids (e.g., crude oil and natural gas) have been produced from the earth, the back end of the fuel cycle takes the produced raw petroleum fluids and refines the.se fluids into useful products. 

Producing companies locate the subsurface petroleum resources recover the oil, gas or condensate and then market the recovered resource to customers. These activities involves planning and carrying out exploration, drilling and well completion, and the production activities. 

This chapter describes the various auxiliary equipment that are important to the function of oil field activities. This equipment is used in drilling, well completion, production, and related operations. The discussions that follow will concentrate on the basic operation characteristics and specifications required by a user. The aim is to give the user the information needed to ascertain whether the equipment available for a particular field operation is adequate, or if the equipment available is not adequate, how to specify what equipment will be necessary. 

Types of Operations 840. Equipment 844. Well Completion 847. Well Control 852. Air, Gas, and Unstable Foam Calculations 853. 

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