Sedimentary facies of Jurassic in 3112 Block, Morondava Basin, Madagascar

3112 Block is located in the southern Morondava Basin, Madagascar, in which systematic studies on sedimentary facies of Jurassic have not been conducted yet. So it is significant to carry out sedimentary facies study to guide... [ view full abstract ]

3112 Block is located in the southern Morondava Basin, Madagascar, in which systematic studies on sedimentary facies of Jurassic have not been conducted yet. So it is significant to carry out sedimentary facies study to guide the identification of the development and distribution of favorable reservoir.
On the basis of regional tectonic and sedimentary background, the study of seismic facies was carried out using seismic data of relatively good quality. The seismic facies of Jurassic including IsaloⅡb Formation, Bemaraha Formation and L. Duvalia Formation are mainly sheet, wedge, progradational, chaotic, domal, and blank reflection. Sheet reflection that indicates open and stable deposition dominates. Wedge and chaotic reflection is distributed in the zone where topography varied and fracture developed. Domal and blank reflection is mainly distributed in downthrown side of major faults.
The single well facies of Wells ME-1 and BRN-1 with drilling of whole Jurassic are analyzed, which is then correlated with well-seismic profile to obtain corresponding relationship of seismic facies and sedimentary facies. It is demonstrated that sheet reflection corresponds to coastal plain, littoral and bathyal facies; Wedge reflection corresponds to delta, fan delta and underwater fan facies; Chaotic blank corresponds to the underwater fan and fluvial facies.
According to the corresponding relationship of single well facies and seismic facies as well as sedimentary facies analysis principle of facies sequence and typical facies, the sedimentary facies of target stratums are elaborated by transformation of seismic facies, combined with the tectonic background. The study indicates that the sea level had risen while coastal plain facies was developed in eastern and coarse clastic sediments deposited near east provenance in the IsaloⅡb sedimentation period in 3112 Block. Bemaraha Formation is characterized by neritic facies in the central, which transited to neritic facies of sandstone and limestone, and then littoral and delta facies symmetrically in both sides. As for the L. Duvalia Formation, neritic and delta facies successively developed.