Petrology and formation damage control, Upper Cretaceous sandstone, offshore Gabon

Abstract

The subarkosic-sublitharenitic Upper Cretaceous sandstone, which has up to 30% porosity and 585 md permeability, produces on salt diapir structures in the Oguendjo West Block, offshore Gabon. The porosity consists of 68% intergranular porosity of primary and secondary origin, 17% secondary intragranular and moldic porosity, and 15% rnicroporosity. A microcrystalline quartz druse, which was derived from alteration of lithic fragments, coats framework grains and retards the development of syntaxial quartz overgrowths. Other cements are patchy ankerite (0.3-13.7 vol%) and kaolinite, which also occurs as a replacement of framework grains. The total kaolinite content ranges from 1.8 to 8.2 vol%. Kaolinite and remnants of altered and partially dissolved lithic fragments are susceptible to movement with fluid flow. Formation sensitivity tests showed that the kaolinite-rich sandstone was stable to 2% NaCI water, but introduction of freshwater caused permeability impairment. Acid treatment to remove damage produced sporadic results. Injection of HCI raised the permeability temporarily, indicating that fines were still being liberated within the pore network. Injection of HCI/HF immediately reduced permeability through partial disaggregation of the rock. Plugging of the formation face by drill mud also damages the reservoir. Reversal of flow at high pressure differentials will remove formation damage produced by face plugging. A guideline for this process established in the laboratory is to backflow with a pressure differential at least as high as the overbalance used in drilling. The combination of oil-based drilling fluids and underbalanced perforating with filtered diesel in the wellbore should eliminate most formation damage in this reservoir.

Understanding Oil and Gas Shows and Seals in the Search for Hydrocarbons

“…One of the best sources on formation damage is that of (King 2009 ) and some of the summaries used in this text are from Thomas ( 2001 ). Some other good references include (Bennion and Thomas 1994 ;Bennion et al 1996 ;Joshi 1991 ;Kasino and Davies 1979 ;Minh et al 2011 ;Pittman and King 1986 ).…”

Petrography and clay mineralogy of volcanoclastic sandstones in the Triassic Rewan Group, Bowen Basin, Australia

“…Some of the clay minerals are fresh-water sensitive (smectite and mixed-layer clays) and some are acid-sensitive (chlorite), whereas others (kaolin) are prone to the effect of the mechanical migration of fines, a problem due to the pressure differentials between the formation and the well during drilling and hydrocarbon production. Kaolin may also cause varying degrees of impaired permeability on contact with fresh water as a result of colloidal dispersion (Pitman & King 1986).…”

“…The timing of cementation, may be important and affect compaction (Pitman & Larese 1991). A cement that forms early does not completely occlude the pore space.…”

Molecular simulation of the adsorption of the hydration inhibitor N1,N1’-(ethane-1,2-diethyl)bis(N1-(2-aminoethyl)ethane-1,2-diamine onto montmorillonite

“…These reserves represent greater resources than other unconventional oil and gas reservoirs. However, wellbore instability (Laffer et al , 1966; O'Brien & Chenevert, 1973; Bol et al , 1994) and reservoir damage (Jones, 1964; Pittman & King, 1986; Wilson & Wilson, 2014) caused by clay hydration and swelling make it more difficult to exploit shale oil resources, leading to significant economic losses. Therefore, inhibiting clay swelling is crucial to ensuring the smooth progress of drilling processes (Ren et al , 2021).…”