Formation perforation

In a new well (or in a recompleted or reperforated well), if perforations are incomplete, then a positive skin value will be present. However, it is present as i pseudo-skin, not as skin due to acid-removable formation damage. The total skin effect may be written as equation (3.3), which refers to the large number of pseudo-skin factors that may exist, including phase- and rate-dependent effects partial completion and slant and incomplete perforations. In equation (3.3), s is the only skin that acidizing can address. 

Acidizing cannot address insufficient, inadequate, incomplete, or inefficient perforation. Reperforating is the only viable option in that case. Hydraulic fracturing may be used if fluid entry is possible. 

Acid-removable damage may be present (or determined to be present), but the right type of acid must be used to remove the damage. For example, HCl will not dissolve plugging solids such as clays and other siliceous fines. HF should not be used to remove calcium carbonate solids or scales other than sihca. 

This requires no explanation. All fluids must be as clean as possible. Source waters used to mix stimulation fluids must be adequately filtered. See chapter 16 for more information about on-site acidizing quabty control practices. 

Additives are discussed in chapter 6. Using additives in excess or mixing additives that are not compatible with other additives in acid can absolutely ruin a treatment. There are many possible additive combinations that can 

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Sometimes primary cementations are not successful, for instance if the cement volume has been wrongly calculated, if cement is lost into the formation or if the cement has been contaminated with drilling fluids. In this case a remedial or secondary cementation is required. This may necessitate the perforation of the casing a given depth and the pumping of cement through the perforations. 

A similar technique may also be applied later in the wells life to seal off perforations through which communication with the formation has become undesirable, for instance if water breakthrough has occurred ( squeeze cementation ). 

The purpose of the well completion is to provide a safe conduit for fluid flow from the reservoir to the flowline. The perforations in the casing are typically achieved by running a perforating gun into the well on electrical wireline. The gun is loaded with a charge which, when detonated, fires a high velocity jet through the casing and on into the formation for a distance of around 15-30 cm. In this way communication between the wellbore and the reservoir is established. Wells are commonly perforated after the completion has been installed and pressure tested. 

The bare foot completion, which leaves an open hole section below the previous casing, is cheap, simple and suitable for consolidated formations which have little tendency to collapse. The slotted liner s an uncemented section of casing with small intermittent slots cut along its length, which prevents the hole from collapsing, but allows no selectivity of the interval which will be produced. The cased and cemented horizontal completion does allow a choice of which intervals will be perforated and produced. None of these examples provides any effective sand exclusion it this is required a gravel pack or a pre-packed liner can be used. 

Cement is then placed across the open perforations and partially squeezed Into the formation to seal off all production zones. Depending on the well configuration it is normal to set a series of cement and wireline plugs in both the liner and production casing (see Figure 16.2), to a depth level with the top of cement behind the production casing. 

The next larger film sizes, considered a medium format, are 120-, 220-, and 70-mm roU films. The first two are about 62-mm wide and unperforated the last is bulk motion-picture stock perforated along both edges. These are also available in a range of emulsion types. 

The tubular positive plate uses rigid, porous fiber glass tubes covered with a perforated plastic foil as the active material retainer (Fig. 2). Dry lead oxide, PbO, and red lead, Pb O, are typically shaken into the tubes which are threaded over the grid spines. The open end is then sealed by a polyethylene bar. Patents describe a procedure for making a type of tube for the tubular positive plate (90) and a method for filling tubular plates of lead—acid batteries (91). Tubular positive plates are pickled by soaking in a sulfate solution and are then cured. Some proceed directiy to formation and do not requite the curing procedure. 

Various methods are used for evaluatiag the quaflty, ie, physical strength and ensyme dust formation, of the granulate. In the elutriation process, a sample of product is fluidised ia a glass tube with a perforated bottom plate for 40 miautes. Dust from the sample is collected oa a filter and the ensyme activity measured. An acceptable dust level is when less than 5—10 ppm of the activity of the sample has been collected. In the so-called Heubach method, 20 g of granulate is elutriated. During the elutriation, four steel balls are rotated ia the bed ia order to evaluate the impact of attritioa oa the dust release of the ensyme. The dust is collected oa a filter and measured. The acceptable dust level is very low. 

Fully cased and cemented with the casing perforated in either competent or somewhat incompetent formations... 

For rayon fiber based eomposites (Seetions 3 and 4) the fiber and powdered resins were mixed in a water slurry in approximately equal parts by mass. The isotropie piteh earbon fiber eomposites (Seetion 5) were manufaetured with less binder, typically a 4 1 mass ratio of fiber to binder being utilized. The slurry was transferred to a molding tank and the water drawn through a porous sereen under vacuum. In previous studies [2] it was established that a head of water must be maintained over the mold screen in order to prevent the formation of large voids, and thus to assure uniform properties. The fabrieation proeess allows the manufaeture of slab or tubular forms. In the latter case, the cylinders were molded over a perforated tubular mandrel covered with a fine mesh or screen. Moreover, it is possible to mold eontoured plates, and tubes, to near net shape via this synthesis route. 

While designing completion/workover fluids the main consideration is given to the effect of the fluids on well s productivity. Low production rates can be due to factors that are unrelated to the fluids introduced to the production zone. These would include poor or shallow perforations, cement filtrate invasion, paraffin wax deposition from crude oil, or movement of formation sand to block the well-bore. 

An injectivity test is performed using clean, solids-free water or brine. If a low fluid loss completion fluid is in the hole, it must be displaced from the perforations before starting the injecting. This test will give an idea of the permeability of the formation to the cement filtrate. 

Hesitation continues until no pressure leak-off is observed. A further test of about 500 psi over the final injection pressure will indicate the end of the injection process. Usually, well-cementing perforations will tolerate pressures above the formation fracture pressure, but the risk of fracturing is increased. 

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