Deciphering the implication of microfacies types and diagenesis on the reservoir quality of the Cambrian sequence in Hassi Messaoud Field, Algeria

The Cambrian Hassi Messaoud sequence is considered a main reservoir in East Algeria and North Africa. It is well represented in the Hassi Messaoud Basin by four units, from base to top they are R3, R2, R1 (Ra and RI units), and alteration zone. Among these, the Ra is the most important unit due to its reservoir potentiality; it is classified from base to top into D4, D3, D2, ID, and D1 reservoirs, while the RI zone is called D5. Due to their importance as oil-producing reservoirs, this study deals with the implementation of the microfacies type and pore architecture on the quality of these reservoirs. A detailed petrographical study and SEM imaging are applied to reveal the pore and grain fabrics, and decipher the dominant clay types and distribution. Also, a detailed study on the flow and storage capacities of 5108 plugs selected from the six Cambrian units, where porosity and permeability are measured and the reservoir quality parameters are also estimated including the flow zone indicator (FZI), the reservoir quality index (RQI), discrete rock type (DRT), and the effective pore radius (R35). Considering these parameters, the studied plugs are summed up into six petrophysical static rock types (PSRT). The PSRT1 has the best reservoir quality values due to its high porosity, permeability, DRT, R35, RQI, and FZI. This PSRT is primarily composed of siliceous quartz arenite microfacies and is highly affected by the dissolution and fracturing as a reservoir quality-supporting diagenetic features. On the other side, the PSRT6 is composed of micaceous and argillaceous subarkose microfacies and is controlled by tight compaction, cementation, and authigenic clay content as reservoir quality-deteriorating diagenetic features. It has the lowest porosity, permeability, DRT, R35, RQI, and FZI values. The PSRT2-5 samples are composed of four microfacies types: 1) siliceous quartz arenite, 2) kaolinitic and siliceous quartz arenite, 3) micaceous, kaolinitic, and siliceous quartz arenite, and 4) micaceous and argillaceous subarkose microfacies. They are affected by various diagenetic features including compaction, cementation, authigenic clay content, fracturing, and dissolution. In general, the whole PSRTs samples are characterized by high heterogeneity in both the mineral composition and the pore architecture. This study is recommended to be followed for delineating the main factors controlling the reservoir quality in various basins, so it may be extendible to the equivalent Cambrian sequences elsewhere.