PETROLEUM GEOLOGY/Production 311 Figure Penetration log correlation and distributions Between 1960 and 1980, most of the presently used production geological methods were developed As a typical example of a classical production geological method, Figure shows a penetration log correlation The different rates of penetration of sandstones and shales (whilst drilling with constant speed and weight) can often be related to spontaneous potential (SP) or gamma-ray (GR) log curves, and thus the progress of wells could be monitored prior to the introduction of modern logging-while-drilling (LWD) much later Further refinements in structural and reservoir imaging came with the spectacular advance of seismic acquisition, processing, and interpretation Seismic attribute analysis is now one of the major production geological techniques Sophisticated borehole imaging logs formed another new source of detailed information The increase in computer capacity also led to reservoir simulation based on complex heterogeneous reservoir models comprising very large numbers of grid cells, which, in turn, required realistic well-calibrated geological models This promoted the use of geostatistical methods and stochastic modelling The present trend is to use a combination of all relevant reservoir data in integrated databases from which visualization can be generated, simulation models can be constructed, and well trajectories can be planned Reservoir Characteristics Influencing Fluid Flow and Storage Capacity Controlling Reservoir Characteristics The quality of a reservoir is directly related to the available pore space (porosity) and the capacity to