This intimate relation between the pressure of gas and the production of oil must be emphasized. Instead of allowing the gas to escape, shut it in, and drill another well lower on the dip for the oil, if oil is the same sand.
Wells making millions of feet of gas which will later be of value must not be sacrificed for momentary considerations. Even where wells are pumped and the pressure is not high enough to cause oil to flow the gas may act as an aerating agent, i.e. make pumping easier. Also the presence of gas tends to bring in the oil from the area around the well. The value of gas has best been appre ciated where air has later been introduced into the wells to form conditions approximating natural conditions. Production has been increased as much as 500 per cent in some of the pools where such methods have been employed. (See Nfixietta or Smith Dunn process, page 195.) A marked example of the efficiency of gas operation may be obtained by a study of the Salt Creek Field, Wyoming. In that field, wells have been flowing for 11 years. The field contains few derricks, only casing-heads and flow-lines show, yet the wells have maintained productions of 100 to 300 bbl. per day at prac tically no expense. These wells are 800 to 1000 ft. deep.
A knowledge of the texture and the specific gravities of the sands guides the production man in the handling of oil. A free open-textured sand will allow oil to flow rapidly into the drill hole. The life of such wells will be shorter than wells with closer-grained sands. Coarse-grained sands have less pore space than close-grained sands.
The specific gravity of oils is an excellent guide in operating. It is well recognized that a heavy asphaltic oil will flow less freely through sands than light oils so that pumping rapidly will drain the sands less quickly.
The effect of offset wells must be fully appreciated. Nearby wells draw production from others. By keeping wells continually pumping the channels in the sand are kept open. If one well stops it is often found that neighboring wells increase in production. If the nearby wells belong to competing companies there is a direct loss, so the careful operator must watch his wells closely, and repair any damages to pumps, or tubing, in his well; or clean out at once, if sand troubles or other troubles occur.
Water conditions bear an important relation to production.
Much water in oil sands reduces the oil production, decreases the quality of casing-head gas, and increases lifting expenses.
Elimination of water trouble causes a material saving, and often a material increase of production.
Methods of combatting water are well understood. Ordinary plugging of oil wells has not been successful. The best methods are careful cementing, proper casing, and mudding-off of sands.
The time to eliminate water troubles is when drilling the wells. If careful drilling and casing methods had been followed in the past most of the water troubles would not have occurred.
Where the oil sand is saturated with water, the oil and gas are driven back into the well and the production declines. This water may be the result of having drilled too deep originally, or be due to water entering the sands from above.
Where water is found in the same sand with oil there is the problem of pumping both together. There may be only 10 bbl. of oil and 90 bbl. of water. Such an amount of water calls for some method of separating oil and water. If the oil separates freely this can be done by simple heating or by stand ing but if an emulsion of oil and water has been formed other treatment is required. The handling of such water in oil wells taxes the ingenuity of oil operators. The suggested remedies are treated in Chap. VII.
Operating production has once been obtained the problem of handling the wells must be taken into consider ation. The problems are of two kinds: 1. Mechanical.
2. Natural.
The mechanical factors are more easily recognized than the natural.
There are three types of wells in oil fields: 1. Flowing oil wells.
2. Pumping oil wells.
3. Wells making oil and gas.
The mechanical equipment and the handling of flowing wells are simple. If the well is a large one and comes in under control the oil will be ejected by pressure through the casing and con ducted to the reservoirs by lead lines or flow lines (see Fig. 40, page 106). Where the well is a small producer and will not flow through the casing it may be induced to flow by putting in tubing and a packer, thus reducing the size of the hole. The reduction in size of the hole creates greater pressure within a smaller space and consequently will force out the oil.