The Characteristics and Distributions of the Carbonate Cements in Braided Fluvial Facies - A Case Study on Mesozoic Reservoirs in Huanghua Depression, Bohai Basin, China

The carbonate cements can always be one of the most important barriers and baffles in the continental depositional systems. Carbonate cements in the form of calcite and dolomite are commonly observed in scanning electron... [ view full abstract ]

The carbonate cements can always be one of the most important barriers and baffles in the continental depositional systems. Carbonate cements in the form of calcite and dolomite are commonly observed in scanning electron microscopic images from the Mesozoic reservoirs rocks in Huanghua Depression. This study aims to determine where the carbonate cements easily sediment and their petrological and geophysical characterizations by using data such as cores, core sample analysis, thin sections, scanning electron microscopy and conventional logging curves. Most of the carbonate barriers and baffles of the reservoirs are calcareous fine sandstone and comglomerate. The carbonate cements consist of ferrocalcite, calcite, dolomite, ferrodolomite, anhydrite, etc.. The spontaneous potential curves are always negative, and the microresistivity logging curve is needle pattern high resistance. An understanding of the diagenetic history and the change of hydrodynamic conditions in braided fluvial facies deposition process may lead to our ability to predict the distribution of carbonate cements across the Huanghua Depression and improve operators’ performance. Three main carbonate cements types were identified:(1)Calcium cemented in the top of the sandstone. They are most likely to develop at the top of the box type positive rhythm channel bar sandstone. (2) Calcium cemented in the bottom of the sandstone. This type of calcareous sandstone most develop on top of bellcurve positive rhythm channel bar sandstone and the top of the box type positive rhythm sand body. This is the most common type.(3) Calcium cemented dispersed interior the sandstone. In the interior of a thick layer of sand, a dispersed conglomeration is formed. (4) Calcium cemented in integral thin layer. With the sand body thickness gradually reduced,the grain size gradually thinning. Fine sandstone deposits in the thin layers are often consolidated by the whole. According to the distribution of the barriers and baffles, the remaining oil can be exploited more effectively.