Introduction This paper presents the results of laboratory and field investigations of the differential separation processing of primary separator liquids to the stock tank. The process basically consists of removing dissolved gases from primary separator liquids by both flash and differential vaporization rather than by conventional flash separation methods. When the gases are so removed stock-tank recovery is increased, since the differential process affords the equivalent of an infinite number of flash separation stages. While the process is applicable to any primary separator liquid, the largest stock-tank recovery increases generally are obtained with rich liquids having a high propane-hexane content. The laboratory phase of the study was concerned primarily with devising a simple method for evaluating the relative merits of the flash and differential processes. Utilization of the method is shown in connection with three primary liquids of widely differing characteristics. Recovery by differential separation was from 4 to 7.5 per cent greater than that obtainable by optimum two-stage flash separation. In one case analyses were made of the tank oils obtained by both processes to determine the distribution of the recovery increase. The laboratory method developed was instrumental in the design of a prototype differential separator for field testing. It was found that a combination flash-differential separation process is essentially as efficient as complete differential separation. Consequently, design simplification of a field prototype was possible, and the diversion of high-pressure gas from sales for operation was unnecessary. The prototype separator used for field testing was constructed to permit either three-stage flash or flash- differential operation. The separator was tested on a condensate well stream. using the alternate methods until sufficient data were obtained for reliable evaluation. Stock-tank recovery increases by the differential process of some 5 per cent were obtained. Concurrent laboratory tests included stage and differential separations and relative weathering rate tests. The laboratory tests generally substantiated the field results, indicating that such tests can be used to evaluate the differential separation potential of a specific well stream. The Flash and Differential Processes The evolution of gas from complex hydrocarbon liquids during a pressure decline may occur by either a flash or differential process. In the flash process gas is evolved as a result of a pressure decline, and it remains in contact with the residual liquid. The composition of the system as a whole does not change in a flash process during the pressure decline. In a differential process gas evolves as a result of a pressure decline and is removed continually from the system. Removal of gas in this manner causes a change in the overall composition of the system. In a complete differential process the pressure decline. gas evolution and gas removal are continuous. The differential process is introduced first in field separation when gas or liquid is removed from the primary separator. In each subsequent stage of separation the liquid initially undergoes a flash vaporization to equilibrium gas and oil, followed by a differential process as actual separation occurs. JPT P. 998^

Because durable pozzolan-cement linings could not be produced by simple, economical methods, efforts were redirected toward sand-cement linings. The results are better linings that have strength, uniformity, and inertness, and that are expected to be long-lived enough to be economical. Introduction "Cement-lined" is the term commonly used and recognized in describing pipe with a lining in which portland cement is the binder for sand or pozzolan. Cost portland cement is the binder for sand or pozzolan. Cost and technical considerations discourage the use of linings made of pure cement. Partial replacement by sand or pozzolan is said to benefit cement and is known to reduce its cost. During the past several years, applicators have cement-lined many miles of steel pipe to carry corrosive water. Oil producers in the Southwest have installed this pipe in distribution systems between water supply wells and waterflood injection wells. The investment in these installations is several millions of dollars. The floods consume large volumes of water from systems that require pipe as large as 24 in. in diameter to supply demands. In and country, there are priorities on potable water, so water for flooding must be obtained from brackish sources. One important source, the Capitan Reef - known locally as the Hendricks Reef - is a prolific aquifer in West Texas, but, as the following analysis indicates, it yields flood water corrosive to steel. pH 6.9 pH 6.9 sodium 3,014 ppm calcium 900 ppm magnesium 292 ppm bicarbonate 400 ppm chloride 4,964 ppm sulfate 2,594 ppm hydrogen sulfide 102 ppm Portland cement combined with sand or pozzolan is a relatively inexpensive lining material and is less affected by this water than is steel. Applicators and users have learned that a particular cement, ASTM Type III containing no tricalcium aluminate, has special resistance to sulfate and other corrosives in this or similar water. The economics of lining pipe requires a rapid means of applying a uniform internal layer of cementitious solids. At present, centrifugal casting is the only feasible method of doing this. In this process a joint of pipe, usually 40 ft long, is mounted in powered rollers. A water slurry with enough solids to form powered rollers. A water slurry with enough solids to form a lining is added, and the pipe is rotated at peripheral speeds of approximately 1,000 linear feet per minute. A minute or two is sufficient spinning time to deposit the solids, compact the layer, and separate excess water. The pipe is then taken to a shed into which steam is injected, and the pipe stays in a moist atmosphere of 120 degrees to 150 degrees F for about 18 hours. Next, the lined joints are flooded with water, capped, and placed in storage where they remain a month or two before going into service. Seventy percent of Type III cement used in linings is tricalcium silicate (C3S, an abbreviation, not a chemical formula). The events of C3S hydration dominate lining technology. As each C3S unit combines with water, it releases two units of lime, Ca(OH)2. JPT P. 51

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