Abstract

Drilling in thin reservoirs is challenging task. But with easy pockets gone the reservoirs left are less than 5 to 10 feet and it becomes difficult to steer well exclusively in the sweet spot or sand in thin payzone. It is this reservoir which offer task to drill horizontal well and produce maximum where otherwise it would be difficult to produce even 200-300bopd from this thin layer of silty shales. Moreover the thin beds are like appearing or vanishing as we drill ahead due to facies change. This needs complete attention till the well reaches Target Depth (TD). Even a small fault of sub-seismic nature of 2 feet throw can offset the well from the sweet zone. But with advanced logging tools used in two wells helps to understand the nature of lithology and its productivity. Best application of this tools are in silty shales in Burgan Sands Upper (BGSU) which generally show high GR and often this leads to misjudgment of well not being in sweet spot.

Logging While Drilling (LWD) logs and inversion was used whether the well is in productive zone or not. The LWD tools now have Azimuthal GR, density and resistivity. This gives a holistic picture of the lithology in the roof side or the bottom side of the lateral section. The wells under discussion were drilled with such advanced version of distance to boundary tool.

After well was steered till TD, the data was processed by Petro-physicist to indicate possible payzone to decide completion. But due to high GR which is often prevalent in Burgan Sand Upper (BGSU) the entire well bore was not getting classified as potential payzone. But after looking the inversion and all LWD data sets it was conveyed that the Inflow Control Device (ICD) can be lowered for entire well bore length. As an outcome advanced ICD was lowered also against high GR zones which otherwise were not getting classified as potential payzone, and well were completed. The well was put on production starting with 1300 BOPD on 32″ choke and still after 18 months continues to produce. PLT results show that the zones indicating high GR and with poor log properties were also contributing oil. The paper discusses these wells and utilization of complete data set acquired at time of drilling and taking completion decision accordingly. The output of data of LWD has been fully utilized to complete the well successfully and given the confidence of doing so in other wells. In fact this experience was used in another similar looking well with unfavorable parameters and successfully completed.

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