Ann: Zapato-1ST Drilling Update, page-68

If we a progressing to TD why no rock chip residue or shows mentioned

Hydrocarbon residues of droplet-scale viscous, or solid, heavy hydrocarbons occur in rocks as coatings on grains and as pore-filling material. Hydrocarbon residues are the result of bonding of hydrocarbons to solid mineral surfaces and/or the degradation of oil to an immobile viscous crude (e.g., by aerobic bacteria) or a burned-out carbonaceous residue. These surface films of heavy hydrocarbons on the rock framework can result from both chemical and physical bondings of hydrocarbons on solid mineral surfaces. Chemisorption occurs when a chemical bond is formed between a hydrocarbon molecule and a mineral surface. An example of such a bond is the sorption of naphthenic acids on the basic mineral surface in limestones. Physical adsorption occurs where surface active, polar hydrocarbons are adsorbed by intermolecular forces on a high-energy mineral surface (such as quartz). These processes can produce a surface film of oil coating the grains in the larger pores of a reservoir rock (Salathiel, 1972).

Transformation of crudes can also produce a viscous immobile heavy hydrocarbon residue in the subsurface. G. T. Philippi (personal commun.) has demonstrated that the phase separation of oil and gas at high pressure produces a viscous asphaltic residue. Deasphalting, the process where asphaltenes can be precipitated out of solution from liquid oils as increasing amounts of gases are dissolved, can also produce an immobile asphaltic residue (Evans et al, 1971). Water washing and biodegradation can alter a liquid crude to an immobile heavy hydrocarbon residue (Evans et al, 1971). Thermal maturation of a crude oil can eventually produce a burned out (thermally dead), or partially burned out carbonaceous residue (anthraxolite). It should be noted that water washing, biodegradation, and thermal maturation could act on both water-displacement residuals and continuous phase oil occurrences.