Text 10

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

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.