Evaluation and prevention of formation damage in offshore sandstone reservoirs in China

Abstract

Reduction in water injectivity would be harmful to the waterfl ood development of offshore sandstone oil reservoirs. In this paper the magnitude of formation damage during water injection was evaluated by analyzing the performance of water injection in the Bohai offshore oilfield, China. Two parameters, permeability reduction and rate of wellhead pressure rise, were proposed to evaluate the formation damage around injection wells. The pressure performance curve could be divided into three stages with different characteristics. Analysis of fi eld data shows that formation damage caused by water injection was severe in some wells in the Bohai offshore oilfi eld, China. In the laboratory, the content of clay minerals in reservoir rock was analyzed and sensitivity tests (including sensitivity to water, fl ow rate, alkali, salt and acid) were also conducted. Experimental results show that the reservoir had a strong to medium sensitivity to water (i.e. clay swelling) and a strong to medium sensitivity to fl ow rate, which may cause formation damage. For formation damage prevention, three injection schemes of clay stabilizer (CS) were studied, i.e. continuous injection of low concentration CS (CI), slug injection of high concentration CS (SI), and slug injection of high concentration CS followed by continuous injection of low concentration CS (SI-CI). Core fl ooding experiments show that SI-CI is an effective scheme to prevent formation damage and is recommended for the sandstone oil reservoirs in the Bohai offshore oilfi eld during water injection.

Reservoir Formation Damage; Reasons and Mitigation: A Case Study of the Cambrian–Ordovician Nubian ‘C’ Sandstone Gas and Oil Reservoir from the Gulf of Suez Rift Basin

“…Such interactions may alter a reservoir's wettability and in turn the relative permeability of the reservoir fluids, leading to negative impacts on reservoir productivity. Therefore, it is advisable to control both the solid and fluid invasion from well fluids to the formation, commencing at the time of drilling of the formation and continuing through all stimulation and workover operations [99,100]. Where, the drilling fluid solids and filtrate invasion are potential candidates and possible sources of initial formation damage [18,21].…”

Pore-Scale Analysis of the Permeability Damage and Recovery during Cyclic Freshwater and Brine Injection in Porous Media Containing Non-Swelling Clays

“…This phenomenon referred to as water sensitivity could occur in both unconsolidated and consolidated geologic materials containing a small percentage of clays, e.g., Refs. [4,[8][9][10][11][12][13][14][15][16][17].…”