A sedimentological approach for an optimal resolution of drilling mud losses

In spite of the geological knowledge accumulated on more than 800 uninterruptedly cored wells during the forty last years, the drilling of the 8" 1/2 diameter phase of Hassi-Messaoud oil field (Algeria) remains delicate because of excavation and drilling mud losses problems. The main objective of this work was to study the problem of drilling mud losses by the use of a sedimentological approach and to localize the producing levels of the subjacent Cambrian. For that purpose, the fast and slow drilling advance zones in the Triassic sedimentary sequences were localized in order to establish distribution maps. Thus, it was highlighted: - that the fast advance zones correspond to the sectors without mud losses (argillaceous facies of the flood plain), whereas the zones with slow advance correspond to the significant mud losses sectors (sandy facies of the fluviatile bars); - that under the fast advance zones of the Triassic series, potential hydrocarbon reservoirs are located.