Abstract

In the last decade, hydrocarbon production from low-permeability reservoirs has been on the rise. Multi-stage hydraulic fracturing is the most common technology used to make production from such reservoirs economically viable. Radioactive-tracers and production logging, which are usually used to assess fracture flow efficiency, do not always provide reliable information in terms of the fracture effectiveness and total frac flow height. An advanced technique described in this paper not only can identify active fractured intervals but also quantify the inflow profile.

A novel technique was developed to locate fracture inflows and quantify inflow profiles in hydraulically fractured wells. It builds on the industry-proven combination of Spectral Noise Logging and High Precision Temperature Logging. This technology was initially implemented for qualitative and quantitative analysis of reservoir flows, including those through leak points, cement, reservoir rock matrix and reservoir fractures. Fracture flow intervals are located using a new-generation of Spectral Noise Logging tool with wider dynamic and frequency ranges. Quantitative inflow profiles are derived by temperature modelling.

The technology described in this paper allowed assessment of hydraulic fracturing effectiveness in the producing wells of Petroleum Development Oman. Three case studies are presented to demonstrate the application of this technology in two producing gas-condensate wells and one oil well, one vertical gas producer and the other horizontal, drilled into clastic low-permeability heterogeneous layer-cake reservoirs and therefore requiring multistage hydrofracturing for commercial hydrocarbon production.

Production profiles were determined for all wells, with inflow splits between producing zones quantitatively analysed using temperature modelling, matching the recorded and modelled temperatures, pressures and phase compositions, and taking into account surface data, such as production history and separator test data, and PVT fluid properties. Spectral Noise Logging was used to determine the frac flow intervals.

In the vertical well, the survey was conducted at three different flow rates to improve inflow quantification by matching three data sets.

The survey results were used to successfully evaluate the effectiveness of multi-stage hydraulic fracturing and fracture height. The acquired information was used to improve hydraulic fracturing planning and design for the field. One of the advantages of applying this technique for fracture flow evaluation is its ability to survey wells under existing operating conditions without shut-in and production deferment. As opposed to conventional production log with spinner, described technique can locate and quantify flow behind pipe.

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