Separation downhole

Tften, other forms of artificial lift are used to produce oil wells such as ( ivnhole submersible pumps and rod pumps that require that most of 1 formation gas be separated downhole and flowed up the annulus... 

The purpose of performing separation downhole is to increase the production rate to the platform, by removing the main part of the water for reinjection. The lowering of the liquid volume will enhance the effect of gas lift, by lowering the slope of dynamic pressure versus gas flow rate, and the reduced produced volume will also reduce the strain on the existing process equipment. Cyclonic separation will, as mentioned earlier, often be constrained by the demand of a water continuous flow. 

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. 

The principle of operation of the hydraulic reciprocating pump is similar to the beam pump, with a piston-like sub-surface pump action. The energy to drive the pump, however, is delivered through a hydraulic medium, the power fluid, commonly oil or water. The power fluid drives a downhole hydraulic motor which in turn drives the pump. A separate surface pump delivers the hydraulic power. The power fluid system can be of the closed loop or of the open type. In the latter case, the power fluids are mixed with the produced fluid stream. The performance of the hydraulic pump is primarily monitored by measuring the discharge pressures of both surface and sub-surface pumps. 

Sand production from loosely consolidated formations may lead to erosion of tubulars and valves and sand-fill in of both the sump of the A/ell and surface separators. In addition, sand may bridge off in the tubing, severely restricting flow. The presence of sand production may be monitored by in-line detectors. If the quantities of sand produced become unacceptable then downhole sand exclusion should be considered (Section 9.7). 

A promising technique currently under development is downhole separation whereby a device similar to a hydrocyclone separates oil and water in the well bore. The water is subsequently compressed into a zone beneath the producing interval and only the oil is produced to surface. 

The rotary shoulder connections must be made up with such torque that the shoulders will not separate under downhole conditions. This is of critical importance because the shoulder is the only area of seal in a rotary shoulder connection. Threads are designed to provide a clearance between crest and root that acts as a channel for lubricant and also accommodates the small solid particles. 

The crude oils were fresh samples from cold separators, or cold treaters, or from a cold tank recently produced into from a cold separator or cold treater, and without the addition of emulsion breakers. As far as is known, downhole corrosion inhibitors... 

The downhole heaters are of two types (a) fuel-consuming flame heaters and (b) electric. The flame heaters, in turn, can be of two subtypes (a) diffiisors, in which the fuel and the oxidizer are brought into the combustion chamber separately and (b) mixers, in which the flammable mixture is brought into the combustion chamber already preprepared. 

The heaters of the type illustrated in Fig. 56 can be built to bum different forms of liquid fuel such as crude oil, fuel oil, or diesel fuel. The heater is lowered to the bottomhole through the production tubing. Once it is in place, the fuel-air mixture is pumped downhole under a certain amount of required pressure. During the treatment the pressure can be regulated from the surface within a broad range. Prior to entry into the combustion chamber the fuel-air mixture is run through a separator. 

In surface emulsion treaters (e.g. oil-water separators), the occurrence of foams is generally undesirable and any such foams will have to be broken, either downhole or at the surface [12, 15). Oilfield-produced water may also foam, which can also cause problems in handling and in gas separation. This is usually dealt with by adding antifoaming or defoaming chemicals such as silicones, polyglycol esters or polymers such as polyfethylene oxide)—polyfpropylene oxide) block copolymers. 

GI Olsen. Offshore Downhole Oil/Water Separation-DOWS — Humble Testing. Oslo Kvaemer Oilfield Products, 1998, p 48. 

The injection system is the portion of the field that is responsible for injecting water (in the case of a waterflood) into the formation. The source of the water that is injected may be a surface water source, such as a lake, river or ocean. If this water has never been injected downhole or come in contact with hydrocarbons, it is referred to as fresh water. Water that is produced from the formation along with oil and gas is referred to as produced water. Produced water is separated from the oil and gas by the action of a series of separators in the production system. The production system will be discussed in detail below. A simplistic diagram of an injection system is shown below in Figure 1. 

A mathematical model was developed to describe the effect of viscosity on the stability of fiber-containing drilling fluid sweeps. In order for the fiber to perform as efficiently and effectively as possible as a hole-cleaning aid, it is important that the fiber be homogeneously distributed throughout the base fluid, i.e. minimal separation of the fiber occurs under downhole conditions. Thus, a theoretical study was conducted to determine the desirable base fluid properties to formulate sweep fluids that are stable under downhole conditions. 

Typically, there is a trade-off to be made between a rural site which has low cultural seismic noise but is less secure due to its isolation and a secure urban site, such as police or fire station, which has higher cultural seismic noise. Ideally, an operator wants a low cultural noise site that is also secure. With downhole installations, a secure urban site enables the reduction of seismic noise by providing vertical separation from seismic noise which originates at the surface. The degree of attenuation of seismic noise with depth will depend... 

Produced water contains hydrocarbons in the form of dispersed oil droplets, which, under proper conditions, can be coalesced into a continuous hydrocarbon liquid phase and then separated from the aqueous phase using various separation devices. The diameters of these oil droplets can range from over 200 pm to less than 0.5 pm and may be surrounded by a film (emulsifier) that impedes coalescence. The relative distribution of droplet sizes is an important design parameter and is influenced by the hydrocarbon properties, temperature, downhole operating conditions, presence of trace chemical contaminants, upstream processing and pipe fittings, control valves, pumps, and other equipment that act to create turbulence and shearing action. These oil droplets are collectively defined as "dispersed oil."... 

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