Formation stimulation

After a well is completed, the production rate may not be high enough. A common cause of this is low permeability of the reservoir. To raise the production rate, the well will have to be stimulated. There are many ways of stimulating a formation, but the main ones are hydraulic fracturing and acidizing.

These processes are often used in combination since they frequently help each other. Programs for individual wells vary according to well characteristics and conditions, and end result desired.

Fracturing is a process by which fluid pressure at the bottom of a well is built up by high-pressure pumps to the extent necessary to overcome the weight of rock above plus an additional pressure required for actually breaking (cracking) the formation, thereby making possible the introduction of fluids carrying sand, walnut hulls, or other small particles of material into the new openings created to keep the fractures open. The purpose of fracturing is to open existing fractures to increase the flow of the reservoir fluid into the well bore. When the pressure is released, however, the cracks must be kept open. For this reason, propping agents are carried in the gel and are left behind to hold open the cracks. The most common propping agents are rounded sand grains, glass beads, and walnut shells.

Acidizing is a process by which acids are applied to the producing formation to enlarge existing passages, or are forced into the pores of the formation to increase the production rate of the formation. Acidizing can be used to stimulate reservoir rock, which is soluble in acid. By dissolving the formation, the acid opens up and enlarges fissures in the rock around the borehole. In order to stimulate reservoirs consisting of limestone and dolomite, hydrochloric acid (HCl) is generally used. Hydrofluoric acid (HF) is used to stimulate certain kinds of sandstone reservoirs. It is also used to clean up pore spaces, which have been blocked by drilling fluid clay.

Text 11

Read, translate the text "Tank gaging" and make the annotation of it.

Tank gaging

Duties of oilfield operator include measuring the proper amount of oil or gas from wells. In some cases, particularly where stripper wells are produced, as much oil or gas as possible is produced from each well. In many fields, oil or gas is produced from each well in accordance with allowables usually set each month by state regulations based upon the market demand for oil or gas and the efficient rate of production for the particular field and wells. In the absence of such regulations, the amount produced is determined by the individual producer in accordance with his own ideas as to the proper rate of production.

For production-control purposes, the volumes of oil, gas and salt water produced by each well cluster are usually checked or measured by the field operator over each 24-hour period. In any event, when a full tank of oil is delivered to a pipeline, tank car, or tank truck, the oil delivered is measured by gaging the height of oil in the tank before and after the delivery is completed. At such time the oil is tested to determine its density, because often its value depends upon density. Also, the temperature of the oil and its content of BS&W are determined, so that the tank gages can be converted into net barrels of oil delivered at the standard temperature of 600F.

To measure the level of oil in a tank, a steel tape with a plumb bob on the end is lowered into the tank until it just touches the tank bottom. The tape is then withdrawn and the highest point where oil wets the tape shows the level of oil in the tank. By referring this value to the tank table, the volume of oil (or oil and water) in barrels in the tank is determined.

Some use has been made in recent years of automatic tank gages. This device consists of a steel measuring line contained in a housing, with a float on the end of the line resting on the surface of the oil in the tank. The line extends up over the top of the tank and down the outside through a reading box. The end of the line is coiled below the reading box, which is located at convenient height for reading from the ground. The line running through the box is marked to show height of oil in the tank, which can be read through a glass window in the box. This type of device can be further adapted to obtain a continuous recording of tank gages.

Text 12

Read, translate the text "Pipeline valves" and make the annotation of it.

Pipeline valves

Pipeline valves are designed to control flows of oil transported through pipelines. Valves are divided into three classes: stop valves, control valves and safety valves.

Stop valves (gate valves) are used to fully close pipeline flow area, control valves (pressure controllers) - to change pressure or flow rate of pumped fluid, safety valves (check valves and relief valves) - to protect pipelines and equipment when acceptable pressure is exceeded, and also to prevent fluid back flows. Gate valves are stop devices, in which flow area is closed by the gate forward motion in direction at right angle to oil flow. By design a gate valve represents an integral cast or welded body equipped with two nipples to connect to a pipeline (by means of flanges or welding) and a stem connected to a stop element and controlled by means of a hand wheel or a special actuator. Place of the stem outlet from the body is packed with sealing.

Devices used for automatic maintenance of pressure at the required level are called controllers.

Devices preventing pipeline pressure increase above the set value are called safety valves. Safety valves of closed type releasing a part of fluid from the place of higher pressure origination are used on oil lines. Device for prevention of fluid reverse flow in a pipeline is called a check valve. Swing check valves with the gate revolving on its horizontal axis are used for oil pumping.

Text 13

Read, translate the text "Refineries" and make the annotation of it.

Refineries

In general, refineries are divided into simple and complex, but analysts also often use the term «very complex».

Simple refinery processes include distillation of crude oil, hydro treatment of intermediate distillates and catalyst reforming of naphtha.

Complex refinery processes include the same plus catalyst cracker and alkylation and gas fractionation plants.

Very complex refinery processes include the same what is performed at the complex refinery plus units to produce defines or to crack residue (for example, coking unit).

Refining of any crude oil at the very complex refinery produces more light petroleum products than at the simple refinery.

In standard industry model volumes of petroleum products can be calculated for each type of crude oil at each type of refinery. This helps to find out how efficient can be refining of specific type of oil for specific type of refinery. For that purpose calculation results are reviewed with two different methods: making «a snap» of general industry picture and studying dynamics of situation changes in its components.

Modern communication means and computer technologies provide for an opportunity to weekly calculate and issue data that assist in evaluating commercial interest of buyers in various types of crude oil. Two geographical points are accounted - the point where prices for petroleum products are fixed and the point where the price for crude oil is fixed. The prices for the petroleum products are normally fixed in the place where the crude is refined. The price for the crude oil can be fixed in the same place but also can be fixed in the place where the crude is produced.

Text 14

Read, translate the text "Migration and Accumulation of Petroleum" and make the annotation of it.