Breakthrough water

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 dissolution of carbonates can create spectacular features like those found in many caves. The process is termed karstification. Some reservoirs are related to Karst. Examples are the Bohai Bay Field in China or the Nang Nuan oil field in the Gulf of Thailand. These reservoirs are characterised by high initial production from the large open pore system. However, since the Karst features are connected downdip to the waterleg this is usually followed by rapid and substantial water breakthrough. ... 

These results would be interpreted as showing that water breakthrough has occurred earlier in layer B than in the other layers, which may give reason to shut off this layer (as discussed below). The lack of production from layer C may indicate ineffective perforation, in which case the interval may be re-perforated. The lack of production may be because layer C has a very low permeability, in which case little recovery would be expected from this layer. 

When water is injected into a water-wet reservoir, oil is displaced ahead of the injected fluid. Injection water preferentially invades the small- and medium-sized flow channels or pores. As the water front passes, unrecovered oil is left in the form of spherical, uncoimected droplets in the center of pores or globules of oil extending through intercoimected rock pores. In both cases, the oil is completely surrounded by water and is immobile. There is htde oil production after injection water breakthrough at the production well (5). 

Recovery factor calculations may not be possible under certain situations, including (1) a decrease in steam flow rate due to water breakthrough (2) scale deposits in the well-bore and/or fracture conduits (3) a fluctuating flow rate and (4) the completion of additional production wells in injection-affected areas, which will have an impact on the decline rates of nearby production wells. 

There are many factors that nay adversely affect the daily production target, including both scheduled and unscheduled equipment outages associated with the GCs and the pipeline. It is therefore frequently necessary to cut back production in one area of the field and perhaps increase production in another area to compensate. Also, production rate limitations may be placed on individual wells because of reservoir conditions, for example, to prevent gas coning or water breakthrough. All of this is accomplished by adjustment of the flowline chokes. 

With an intact membrane, the penetration of water is very small. It will be correspondingly higher with a damaged membrane and this can even lead to a water breakthrough. 

Abstract. Activated carbon Norit R 08 Extra, and molecular sieve type 4A, were investigated using dynamic (tert-butylbenzene (TBB), cyclohexane (CHX) and water vapour) adsorption methods. The TBB, CHX and water breakthrough plots for fixed activated carbon - molecular sieve beds were analyzed. It was found that the type of bed composition with mechanically mixed activated carbon with molecular sieve, or separated activated carbon and molecular sieve layers, affects the dynamic adsorption characteristics. 

Keywords activated carbons molecular sieve breakthrough dynamics tert-butylbenzene adsorption cyclohexane water breakthrough time... 

Water breakthrough curve on Alcan AA-300 alumina at 50°C. Feed 3370 ppm water ambient pressure. 

The constant pattern water breakthrough curve for isothermal adsorption of trace moisture (Langmuir isotherm) from an inert carrier gas can be described by [15] ... 

Before water breakthrough, only oil is produced, and the volume of oil produced is equal to the water injected. Therefore, the oil recovered at any time to before water breakthrough is... 

Before water breakthrough, the oil recovered at any time tn is given by Eq. 

The selected reservoir should have earlier water breakthrough, high water cut, and low current recovery, and it must have great permeability contrast in layers. 

Field test data show that a typical amount of surfactant injected in Cs (in %) x injection PV (in %) is about 10 to 12 (see Section 13.8). The minimum chemical mass injected should be just about the retention. The rule of thumb is about 20 to 50% more than the retention. According to the work of Trashenski et al. (1974), to prevent water breakthrough polymer and the polymer breakthrough micellar solution, the polymer volume requirement is about 0.5 PV. 

Solids production can be classified (24) as transient, continuous, or catastrophic. Transient solids production refers to situations where the concentration of produced solids decreases with time. This type of solids production is typical of well cleanup after completions or workovers and after water breakthrough. Continuous production occurs when some low level of solids production is tolerated. Typical levels for continuous solids production are 6-600 g/m3 of fluid (24), a solids cut of less than 0.06%. Continuous production of solids with heavy oil from unconsolidated sandstone reservoirs can exceed 50% solids cut (25). Catastrophic solids production is caused by an event that allows a large slug of solids into a well, completely blocking the producing zone. 

Solids production can be triggered by water breakthrough. This reduces the capillary forces between the grains, which then can be dis-... 

Figure 9. Failure envelopes and critical maximum drawdown with influence of water breakthrough and massive shear failure. (Reproduced with permission from reference 49. Copyright 1991 Society of Petroleum Engineers.)...

In this paper, based on a verified microscopic capillary model, a semi-empirical strength model, and a coupled elastoplastic geomechanics model, the effects of capillarity, chemical reactions, and pore pressure are considered and incorporated into stress calculations. The results reveal which processes play major roles in destabilizing sand in oil/water fluid environments at different stages of water breakthrough. 

Biphasic fluid conditions in porous media (i.e. oil-water, oil-gas, gas-water) generate liquid menisci among particles, whence weak capillary forces arise to cohesively bond particles. Some doubt the significance of capillarity on rock stability (Lord et al., 1998) others believe it plays an important role in sand production after water breakthrough into an oil well (Papamichos et al., 1997 Bianco and Halleck, 2001). 

After water breakthrough, two pressures exist water pressure and oil pressure. Assuming steady-state fluid flow in an infinite reservoir, they can be calculated by... 

Before any further calculations, the water saturation in the microscopic model developed above should be calibrated to experimentally determined values. The saturation discrepancy between the model and reality results mainly from two sources that the microscopic model cannot address one is connate water saturation (Swc) and immobile oil saturation (Sd) the other is the wettability effect of irregular particle surfaces. If we assume that water saturation remains as a constant (S g) until water breakthrough occurs, the calibration can be carried out as... 

Skjaerstein A., Tronvoll, J., Santarelli, F.J., Jpranson, H. Oct. 1997. Effect of water breakthrough on sand production experimental and field evidence. SPE 38806, the SPE Annual Technical Conference and Exhibition, San Antonio, TX, USA. 

---