Hadexun oil field, located onshore west China, has been in production for over 13 years. Most of the primary oil was produced from relatively thick oil reservoirs. The development plan has now shifted toward the new resources in previously unexploited reservoirs: the ultrathin reservoir with only 0.4 to 0.8 m thickness and the 1- to 2-m low resistivity pay reservoir with an incoherent bottomwater level throughout the field.

A successful drilling strategy was developed that used double-step long horizontal drilling to cover dual thin layers from a single lateral for the ultrathin reservoir and a medium single lateral for the thin low resistivity pay reservoir. An integrated while-drilling application included directional electromagnetic and wellbore imaging technologies for rigorous geological well placement and spectroscopy and sigma for lithology and fluid identification for advance formation evaluation. This integrated application has enabled us to eliminate the need for pilot-hole wells, cover dual layers by single lateral, and avoid side tracks, thus improving efficiency and significantly saving the AFE budget; accurately place the well and significantly reduce the probability of erroneous lateral placement along the thin target layers and avoid drilling into water zone, thus optimizing reserve recovery; optimize the outline of future horizontal drain locations; and economically develop the new resources in previously unexploited reservoirs.

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