Permeability From Production Logs - Method and Application

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractEstimation of effective permeability at the reservoir scale has been a long standing challenge in carbonate fields. The carbonate depositional and diagenetic history can be quite complex, and this can lead to a permeability field which is quite difficult to characterize. Permeability in vuggy or fractured intervals can be dramatically different from the matrix permeability measured in core plugs. However realistic estimates of oil recovery, and optimized reservoir management requires good estimates of the reservoir permeability.In the Tengiz field, a giant carbonate reservoir in western Kazakhstan, a method has recently been developed to calculate apparent permeability (APERM) based on flow rate from production (PLT) logs. Incorporation of this flow calibrated apparent permeability into the static geologic earth model offers an elegant solution to the long-standing problem of how to best incorporate dynamic PLT data into a reservoir model. A reservoir model recently built using APERM resulted in a step change improvement over previous methods where only static log based permeability transforms were used to populate the earth model.Conventional log based permeability transforms are designed to characterize matrix permeability but not the excess permeability due to fractures & vuggy porosity common in carbonate reservoirs. The APERM method is used for both accurately characterizing total permeability (matrix + excess), and for identifying inaccurate permeability predictions in older wells with poor log quality or limited log data. The log based permeability predictions are more accurate in recent wells with modern logs, but hot streak identification and quantitative permeability estimation from static well logs is still problematic.The apparent permeability is calculated by solving Darcy's law on an interval basis, using as input our knowledge of flowing and static pressures, plus well, reservoir, and fluid properties.The method makes several simplifying assumptions, but the resulting errors are second order in nature, and the method offers improvements over using conventional static log based transform permeability. Application of the method is enhanced by the derivation of coarse scale zonal layer pressures with multi-rate PLTs. Accurate zonal layer pressures improve the accuracy of the permeability derivation. The apparent permeability from PLT is then used as a benchmark to adjust the transform permeability derived from static well logs using a variable multiplier. This technique has the advantage of preserving the original fine scale heterogeneities of the wireline logs, while calibrating their magnitudes. It also has the advantage of identifying higher permeability intervals from rapid changes in well inflow profile, that may not have been characterized by conventional (core plug and wireline) estimates.Recently a full field reservoir model for Tengiz Field has been constructed using APERM data and petrophysical rock types. Preliminary history match results ...

Evaluation of Permeability in Fractured Carbonate Reservoirs by Production Log Tools (PLT)

“…The measured steady flow has about ten percent difference with the surface flow, which is the minimal amount in determining permeability. Skin effect, which has a huge impact on the permeability because this factor affect from several wells [2]. All of interpretation butterfly flow meter logs, is based on the response of flow meter, a linear function of the fluid velocity [10] in the dynamic logging also an assuming done that the fluid velocity and velocity of moving tools are allowed to collect.…”

“…Temperature is constant and flow is laminar. Software by considering these situations with Darcy equation to obtain the permeability [2].…”

“…Logarithmic graph of detection pressure to ensure that get to the radial flow period with unlimited performance before the pressure build up is applied, then the flow rate and pressure data can be analyzed by transient pressure analysis software, with this procedure an interpretation model was built that can be extrapolated the stable well flowing pressure was used ( Figure 6) [2].…”

“…Therefore, recently the use of production log methods to determine the permeability was presented. Production logs suggested when the well was in steady-state and current can be considered as single-phase with the homogeneous environment [2]. This method is suitable in sandstone reservoirs, but this method used in carbonate reservoirs for progress in obtaining permeability.…”

“…In Tengiz reservoir in the West of Kazakhstan with using of production logs the volume of permeability by solving Darcy law in the different well intervals, using flow pressures and static pressure, in addition well properties, reservoir, and fluid as Input measured in throughput. Models of production log data provide reliable estimates for the injection of gas in the Tengiz platform [2]. Recently in Iran with uses of production logs to determine extra water production in Ahvaz oil field and sudden increase of pressure in the well in the Aghajari oil field have been used.…”