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This thesis describes how I have researched and developed new methods for the prediction of rock physical properties using genetic algorithms and fuzzy logic (GAFL).  These techniques are improvements on conventional methods providing two original but dissimilar tools for formation evaluation and reservoir characterisation. The premise behind the use of fuzzy logic in this context is that a reservoir can be broken down into several lithotypes, each having characteristic statistical distributions for electrical log values.  Fuzzy logic attempt to uncover the relationships between these distributions.  Genetic algorithms use a feedback technique that assumes a continuous functional relationship between the electrical log values and rock properties, generating and testing equations that fit predicted and observed responses.  Complex non-linear equations are “evolved” until the best fit is obtained.  Genetic algorithms provide the functional form of the equation as well as the constant parameters of the relationship. I have modified conventional GAFL techniques so that they can be more precisely calibrated and applied to geoscience problems more successfully.  This research analysed the characteristics of large data sets from several North Sea and Middle Eastern fields, and led to the design of software that automatically calibrates GAFL in a way that is less sensitive to noise and data outliers.  I describe the applications of these new techniques to permeability, litho-facies, porosity and shear velocity prediction;  the repair of poor electrical logs and the modelling of shaly sand equations. Permeability governs the movement of fluids through reservoir rocks and is therefore a critical input into reservoir models.  Permeability estimation is extremely challenging, as it is difficult to measure directly using current sub-surface logging technology.  GAFL was applied to predict permeability in the Northern North Sea oil fields.  The newly developed software provides an important and visual indication of the uncertainty associated with the predicted permeabilities.

Endogenous opiates, the enkephalins, have been identified in the brain and intestine. Their physiological role in the gut has yet to be determined, but since opiates have anti-diarrhoeal actions it was thought possible that they might be involved in the control of mucosal ion transport in addition to their known effects on motility. This possibility was studied using the lq'in vitro' technique of Ussing and Zerahn. Morphine (10^-6 to 10^-4M) induced a significant fall in potential difference (PD) and short-circuit current (I_sc) across stripped rabbit ileal mucosa, with no change in tissue resistance. A maximal electrical response was dependent on the presence of Na, Cl and HCO₃ in the bathing medium. A significant increase in Cl absorption due to a decrease in serosa to mucosa flux was provoked in response to morphine (2 x 10^-5M), accompanied by an increase in residual ion flux (J^R/_net), possibly due to HCO₃ secretion. Na transport was unaffected. Dextromoramide (10^-5M) mimicked the response to morphine, but the inactive isomer laevomoramide (10^-5M) had no effect. Naloxone (10^-6M) inhibited the response to morphine (2 x 10^-5M) and this inhibition was competitive in nature supporting the existence of mucosal opiate receptors. The enkephalin analogue Me-Tyr-D-Met-Gly-Phe-Pro-NH₂ also decreased the PD and I_sc and produced a similar increase in Cl absorption and J^R/_net. This analogue had a more rapid action and provoked a response at a lower dose (10^-8M) than morphine. Tetrodotoxin (10^-7M) inhibited the response to morphine (10^-4M) but blockade of cholinergic, α and β adrenergic and dopaminergic mechanisms had no effect. Morphine (10^-4M) inhibited the secretion produced by three secretagogues, prostaglandin E₂ (10^-5M), acetylcholine (10^-4M) and cholera toxin (1 μg/ml). Adenyl cyclase and cyclic AMP levels were unaffected by morphine, but the electrical response to morphine was increased by omitting Ca^+ + from the medium. Thus these studies provide evidence for the presence of mucosal opiate receptors which may have a physiological role, and demonstrate that opiates enhance Cl absorption and inhibit secretion provoked by three secretagogues. The mechanism of action may be related to an antagonism to intracellular calcium.

The effects of straw burning and drying-rewetting cycles on nutrient availability were studied in an attempt to assess the practical importance of the yearly precropping practice by farmers of burning off excess crop residues and of the seasonal climate of North-East Nigeria. Changes in soil properties resulting from heating three soils up to 700°C and from field burning of straw on three soils were determined. Heating to 250° did not affect soil texture but increased exchangeable NH4+-N, available P, Fe, Mn and phosphate adsorption. A peak of NH4+-N representing decomposed organic N, retained by cation exchange sites was observed after heating at 250°. Soil physical and chemical properties were changed by heating to ≥500^o, resulting in fusion of clay particles into sand-sized particles, decomposition of soil organic matter and alteration of soil minerals with a corresponding increase in non-exchangeable cation status of the soils. The changes observed after field burning of straw were mainly due to deposition of ash; these include a dramatic increase in phosphate adsorption and addition of considerable amounts of inorganic P and exchangeable cations. The availability to maize of the inorganic P returned in ash after field burning or released as a result of laboratory heating of soils was assessed over a 7 day period. The increased P status of the soils after straw burning or heating was not significantly reflected in plant uptake of P but K adsorption was enhanced from the ash. Fertilization of heated and field burnt + overlying ash soil samples resulted in adsorption of P with a corresponding reduction of P concentration in the soil solution and P uptake. The N mineralized after rewetting air-dried clay soils or those containing very low organic matter was insignificant. Investigations also showed that, when dried soils were rewetted, the flush of mineral N was derived mainly from soil organic matter and not from killed microbial cells.

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