308 PETROLEUM GEOLOGY/Production Production K J Weber, Technical University, Delft, The Netherlands L C van Geuns, Clingendael International Energy Programme, The Hague, The Netherlands ß 2005, Elsevier Ltd All Rights Reserved Introduction The geological activities following the discovery of a petroleum accumulation commence with a thorough analysis of the find in terms of structural definition, reservoir rock characteristics, and accumulation conditions This is followed by the selection of appraisal well locations and the study of the results If considered commercially viable, a multidisciplinary team, including specialists of all disciplines in petroleum engineering, designs an initial development plan At this stage, the volume of petroleum-in-place is estimated and a dynamic model is built to test the production capacity and producible reserves of the field, which may be generated by a series of alternative development plans After executing the selected initial development plan, the reservoir model is updated with new data The increasing information on field performance is used to calibrate the model by history matching In certain favourable cases, fluid movements can be observed on additional three-dimensional (3D) seismic data (see Seismic Surveys) Further development activities, such as infill drilling, side tracking, recompletions, or fluid injection schemes, are planned on the basis of the updated model Detailed field studies by integrated teams of petroleum engineers and production geologists are carried out periodically until the ultimate stages of the field life (Figure 1) Reservoir performance is a function of the reservoir characteristics and the petroleum properties The study of reservoir characteristics is the primary task of the production geologist An overview is given of the influence of various reservoir heterogeneities on fluid flow To analyse these characteristics, and to quantify the results, requires a wide range of techniques These cover such a large field of subjects that the work has to be carried out by a group of specialists in seismology, sedimentology, structural geology, geostatistics, and petrophysics In addition, a good understanding of the principles of reservoir and production engineering is required to be able to function successfully in a multidisciplinary team The production geological activities at the various stages of field development have a number of different purposes which all require geological input of some kind (Figure 2) This is illustrated by the different techniques and modelling methods that are employed at each stage (Figure 3) The pace of development of new techniques, in particular integrated computer systems, is very fast As a result, the production geological activities are centred around workstations being served by a database containing all relevant information (Figure 4) Historical Development of Production Geology Production geology as a separate petroleum engineering discipline was only generally recognized in the 1950s Early field development, with shallow, closely spaced wells and only cuttings and surface outcrop observations, provided little scope for reservoir studies In the USA and Russia, where grid drilling was and still is in fashion, most companies did very little production geology work in the appraisal stage In Indonesia, where complicated structures were encountered, the need was felt for more geologist involvement at an early stage Around 1915, the Bataafse Petroleum Company (Royal Dutch) started to engage mining engineers with the particular task to improve cooperation between production and geology to achieve a more efficient exploitation of the field The reports from that time show that structural interpretation and detailed mapping of the producing horizons constituted the main tasks In these pre-logging and pre-seismic days, correlations were carried out with the aid of cuttings glued to narrow planks The wireline logs developed by the Schlumberger brothers in 1927 progressively replaced these early methods Just before World War II, effective reflection seismic methods came into use, although any sophisticated processing had to wait for the availability of more powerful computers after 1960 This is also the time that production geology, also called ‘development geology’, began to be more generally employed, although, in most companies, the geologists were still firmly attached to the exploration departments In the meantime, sedimentology had made great strides forwards and more attention was given to the internal architecture of the reservoir Core descriptions and analysis were improved Research studies of outcrops and recent sedimentation of both