|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Steam generation for the purposes of thermal recovery includes facilities to treat the water (produced water or fresh water), generate the steam, and transport it to the injection wells. A steamflood uses high-quality steam injected into an oil reservoir. The quality of steam is defined as the weight percent of steam in the vapor phase to the total weight of steam. The higher the steam quality, the more heat is carried by this steam. High-quality steam provides heat to reduce oil viscosity, which mobilizes and sweeps the crude to the producing wells.
Treatment evaluation leads to problem identification and to continuously improved treatments. The prime source of information on which to build an evaluation are the acid treatment report and the pressure and rate data during injection and falloff. Proper execution, quality control, and record keeping are prerequisites to the task of accurate evaluation. Evaluation of unsatisfactory treatments is essential to recommending changes in chemicals and/or treating techniques and procedures that will provide the best treatment for acidizing wells in the future. The most important measure of the treatment is the productivity of the well after treatment.
The key operations needed are separation, injection, and pumping. A description of the technologies in each area suitable for downhole processing is provided below. The most common method of separating liquid (oil or water) and gas is by density difference. Because of the relatively large differences in density between liquids and gas, this separation is normally easier than oil/water separation, where the densities of the phases are much closer. In a conventional vessel, the force of gravity allows liquid droplets to settle from the gas within a designed residence time.
Many oilfield processes normally employed on the surface may be adapted to downhole conditions. Examples include phase separation, pumping, and compression. Sometimes the design specifications for downhole processes may be looser than surface processing because control is more difficult. Partial processing, in which fluids are separated into a relatively pure phase stream and a residual mixed-phase stream, are most common. Downhole separation technology is best suited for removing the bulk (50 to 90%) of the gas or water, with downstream surface or subsea equipment being used to "polish" the streams for complete separation.
As with most technology, proper candidate selection is key to success. The economics are often determined by the number of and locations of the wells and by the overall geographical development plan. It is important to recognize that downhole processing is not a substitute for prudent profile control of wells through workovers, gel polymer treatments, cement squeezes, and so on. The following discussion applies to both gas/liquid and water/oil processing, followed by sections that discuss screening criteria specific to each. From an equipment standpoint, gas/liquid separation is much easier than oil/water separation. This generally means that it is a more robust application. All separation and pump equipment has an expected lifetime that is typically much shorter than the lifetime of the well. The cost of replacing or repairing the equipment must be considered as well as the initial capital cost.
DNA fingerprinting (also called DNA typing) involves isolating and creating images of DNA (deoxyribonucleic acid) sequences. In the context of reservoir characterization, DNA samples from microorganisms found living in crude oil are examined. The process for creating a DNA fingerprint consists of first obtaining a sample of cells containing, extracting the DNA from the sample, and purifying the DNA. Fragments of different lengths are produced then sorted by placing them on a gel and subjecting the gel to an electric current in a process called electrophoresis: the shorter the fragment, the more quickly it will move toward the positive pole (anode). After electrophoresis, the sorted, double-stranded DNA fragments are subjected to a blotting technique in which they are split into single strands and transferred to a nylon sheet.
All oil fields under waterdrive, either from waterflood or a natural aquifer, eventually produce water along with oil. Even gas-cap and depletion reservoirs may produce some water. For these reasons, as well as economics, excess water production is not desirable. The material presented in this section that deals with water control technology has been abstracted from a detailed review of water problems and control technology. This review contains the references to the original literature.
Cold heavy oil production with sand (CHOPS) involves the deliberate initiation of sand influx during the completion procedure, maintenance of sand influx during the productive life of the well, and implementation of methods to separate the sand from the oil for disposal. No sand exclusion devices (screens, liners, gravel packs, etc.) are used. The sand is produced along with oil, water, and gas and separated from the oil before upgrading to a synthetic crude. To date, deliberate massive sand influx has been used only in unconsolidated sandstone (UCSS) reservoirs (φ 30%) containing viscous oil (μ 500 cp). It has been used almost exclusively in the Canadian heavy-oil belt and in shallow ( 800 m), low-production-rate wells (up to 100 to 125 m3/d).