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. The inward differential pressure difference that will result in part of the filter cake being removed from the face of the formation (usually over the most permeable and higher pressured sections).
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. The layer of solids stranded on the face of permeable formations by liquids driven into the rock by pressure differential towards the formation. When sized correctly the filter cake may completely stop losses.
Figure 1.2--Open vs. closed circulation systems. Lowhead drilling is drilling with the hydrostatic head of the drilling fluid reduced to a pressure marginally higher than the pressure of the formations being drilled. The hydrostatic head of the fluid is maintained above the formation pressure, and reservoir inflow is avoided. Lowhead drilling may be undertaken in formations that would produce H 2 S or would cause other issues if hydrocarbons were produced to surface. It is important not to forget the business driver behind the technology.
It is evident that, to quantify formation damage and to study its impact on hydrocarbon production, one must have reasonable estimates of the flow efficiency or skin factor. Several methods have been proposed to evaluate these quantities for oil and gas wells. The most common methods are multirate tests, isochronal gas-well tests, and transient well tests (pressure-buildup analysis). Multirate tests can be conducted on both oil and gas wells. In these tests, several stabilized flow rates, qi, are achieved at corresponding stabilized flowing bottomhole pressures, pwf. The simplest analysis considers two different stabilized rates and pressures.
Perhaps the most common formation damage problem reported in the mature oil-producing regions of the world is organic deposits forming both in and around the wellbore. These deposits can occur in tubing, or in the pores of the reservoir rock. Both effectively choke the flow of hydrocarbons. Table 1 shows the gross composition of crude oils, tars, and bitumens obtained from various sources. More degraded crudes, including tars and bitumens, contain substantially larger proportions of resins and asphaltenes.
Since the most common use of matrix acidizing is the removal of formation damage, it is important to understand the nature of the damage that exists so that an appropriate treatment can be designed. Well testing and well test analysis generate a skin factor and well completion efficiency. This is insufficient alone for formation damage diagnosis. Well performance analysis has provided a beneficial tool to identify the location and thickness of damage at flow points in the near wellbore area. Models of flow into perforations and gravel-packed tunnels provide a way to relate the location and severity of damage to the completion procedure that preceded it.