Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. An erosion resistant covering or main pipe that is used when tubing is set deeper than the perforations or on the long string across from the upper perforations in a side-by-side completion.
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. A hole made through the casing and cement and into the formation. It has a characteristic entrance hole and penetration. It is the flow path from the formation to the wellbore in a cased and cemented completion.
While typical production operations seek to prevent sand production, cold heavy oil production with sand (CHOPS) operations use sand production to increase overall productivity. This difference can create operational issues throughout the life of a CHOPS well. It has implications for monitoring strategies as well. To initiate sand influx, a cased well is perforated with large-diameter ports, usually of 23 to 28 mm diameter, fully phased, and spaced at 26 or 39 charges per meter. More densely spaced charges have not proved to give better results or service, but less densely spaced charges (13 per meter) give poorer results. More densely spaced charges may eliminate reperforating as a future stimulation choice because full casing rupture is likely to take place.
In most operations, dissolved gas begins to evolve as free gas when the pressure drops as the fluid moves toward and then enters the well. Depending on the fluid properties and gas volumes, the free gas may coalesce and flow as a separate phase, or, as in the case of many heavy oil wells, it may remain trapped as discrete bubbles within the liquid phase (foamy oil). Gas entering the pump causes an apparent decrease in pump efficiency because the gas occupying a portion of the pump cavities is normally not accounted for in the fluid volume calculations. The pump must then compress the gas until it either becomes solution gas again or it reaches the required pump discharge pressure. The best way to reduce gas interference is to keep any free gas from entering the pump intake.
Unlike traditional density logging, focused gamma-ray density-logging tools focus on the density of the wellbore fluid. The focused gamma-ray density-logging tool incorporates a compacted slug of Cesium-137 at the bottom of an open cage. The Cesium emits gamma rays, and a lead lens focuses gamma rays in a narrow beam brllel to the axis of the cage. Because the cage is open, wellbore fluid is present inside the cage, and the fluid is in the path of the focused beam. The gamma rays have an energy level low enough that the rays are deflected by the electron cloud surrounding the nucleus of any atom.
Bullet gun, abrasive, water jets, and shaped charges are perforating methods used to initiate a hole from the wellbore through the casing and any cement sheath into the producing zone. Bullet speed exiting the barrel is usually approximately 900 m/s (3000 ft/sec). Penetration is easiest in low alloy, thinner walled pipe [H-40, to K-55, and L-80 American Petroleum Institute (API) casing series pipe grades]. Penetration in higher strength casing alloy pipe and harder formations is more difficult in most cases and not feasible in others. When successful, the bullet creates a very round entrance hole but may often create a hole with sharp internal burrs.
The most important consideration in selecting a perforator is choosing a gun system that matches the requirements dictated by the completion. On the larger diameter, thick-walled guns, there is much less distortion than on the small, thin-walled through-tubing guns. In wells in which clearances between the gun and tubulars are critical, the amount of distortion of the gun should be determined from the service company before the gun is used. Figure 1 shows a gun swell after firing in a low-pressure test. Gun bowing is often noted in small guns of 2 1/8 in. Figure 1--Gun swell after firing in a low-pressure test.
Perforations from shaped charges (the most common method) are tapering tubes of usually less than 0.8 in. Primary flow from the formation is through the end and walls of the tube. Flow behavior typically is dominated by radial flow with some pseudoradial character in longer perforations. Many early studies ignored the damage around the perforation tunnel and focused on the importance of length and entrance hole diameter. Putting damage effects aside, the length of the perforation tunnel is theoretically the most critical factor in a natural completion in which no further stimulation or sand control is planned. Entrance hole diameter becomes more important when some sand control completion designs are planned or fracturing is needed. Because of the early studies that ignored the effects of formation damage, the primary selling points of perforating charges became perforated length and entrance hole diameter.