Understanding the actual inflow distribution across the reservoir interval is valuable for optimizing reservoir management decisions. It is common to have varying levels of uncertainty in the petrophysical prediction of the inflow distribution. The inflow distribution assessment drives many aspects of the field development plan. A technique is presented for acquiring quantitative measurements of the inflow rate of various reservoirs or layers of a reservoir at various times in the life of the well using interventionless technology.
Chemical tracers are embedded in sand screens that are positioned adjacent to reservoir layers at different depths of a well such that fluid exposure causes release of a unique chemical compounds into the oil produced from each layer. Analysis of the transient behavior of each of the chemical compounds from samples of the produced oil provides a quantitative assessment of the rate of inflow occurring from the adjacent reservoir section. The chemical tracer based measurements of inflow are compared to the petrophysical predictions of inflow distribution. The petrophysical rock and fluid properties are determined using tools such as LWD and core analysis. It is common for these sources to contain uncertainty in their assessments of the inflow potential. The chemical tracer technique provides an assessment of the actual inflow distribution that can be compared to the petrophysical prediction. This additional input is very valuable in reducing the uncertainty in the overall reservoir performance assessment.
Case histories from two wells in frac-packed wells are presented. Both wells had substantial uncertainties in the petrophysical assessments of the inflow performance of layers in the reservoir. The results from the chemical tracer technique provided insight that led to high value decisions. In Case History #1, the chemical tracer showed a layer to be contributing non-commercial rates. The petrophysical based prediction of inflow indicated this zone was of lower quality than the other zones but it was decided to complete the zone as there was possibility of producing economic rates. Significant savings will be realized in future wells by not completing the non-commercial layer. In Case History #2, the overall productivity of the well was substantially below predictions of the petrophysical data. The chemical tracer inflow profile showed all zones producing similarly. The assessment of similar inflow in each layer implied the kh prediction from LWD to be overly optimistic. This insight changed the production profile forecast for future wells. This insight also prevented the need to perform an expensive PLT log in the well to determine if the entire interval was flowing.
Measuring the actual inflow distribution across the reservoir interval in deep, frac packed wells is usually so impractical or prohibitively expensive that it is never performed. The technique presented of using chemical tracers embedded in the completion components provides an on-demand, low cost and minimal risk means of assessing the actual inflow distribution. The inflow distribution information is combined with other data sources to reduce the uncertainty of reservoir management decisions.