Abstract Braided fluvial reservoirs form some of the world’s giant oilfields and are found in many petroleum provinces. At best, they have excellent characteristics, but where non-net intervals (shales and siltstones) form higher proportions, they are more difficult to appraise and develop. Geological characterization (lithological correlatability, vertical sequence and porosity/permeability variability) must be communicated effectively to the reservoir engineer, whose role is to formulate a development plan and predict the production profile for a field, and to monitor and optimise day-to-day field performance. He has at his disposal other techniques: cased hole neutron logging to monitor contact levels; well testing to determine reservoir flow capacity, boundary and layering effects; production logging to assess well inflow performance or injectivity; wireline pressure profiling, field pressure and production history analysis to define vertical permeability and to reveal reservoir compartmentalization and/or communication with aquifer or injected fluids. Computer reservoir simulation modelling, now an essential tool for management of most major fields, has provided the impetus for advances in geological reservoir characterization. The question is: how can we adequately represent braided fluvial reservoirs in such models? At one end of the spectrum, sheet sands (although laterally variable) can be adequately mapped and modelled as ‘layered’ systems based on conventional approaches. At the other are multiple low-sinuosity channel sand reservoirs which, being uncorrelatable at well spacings typical during appraisal of offshore fields, may be suitable targets for stochastic or network — type approaches. Although the behaviour of a hydrocarbon reservoir must be controlled at least in part by its sedimentological characteristics, the engineer’s view of a field may be somewhat different to that of the geologist. This is as true for braided fluvial reservoirs as for those of other environmental origin. The geologist and reservoir engineer must be fully aware of each others’ data, analytical methods and objectives in order to avoid wasted effort. In the future, despite greater computing power and better modelling software, specialist technical disciplines must not loose sight of the overall objectives of field development. Small-scale geological variability affects the viability of enhanced recovery processes such as miscible flooding. However, at the development planning stage, more generalized parameter assessments may be sufficient. Reservoir characterization at the small scale, such as geostatistical outcrop analogue studies, should be balanced by more geological involvement in the planning and interpretation of well tests, which often provide the only dynamic data available during the appraisal and development planning of offshore fields. Greater cross-disciplinary understanding of reservoir characteristics could in turn ensure that an engineer would not develop an incorrect view of a braided fluvial reservoir, perhaps by correlating shaley intervals which just happen to be present at about the same location in the section.

A review of braided fluvial hydrocarbon reservoirs: the petroleum engineer's perspective

Sampling While Drilling: An Emerging Technology

A method and system for statistical pressure gradient and fluid contact analysis. The method and system include planning for a pressure gradient test by using expected parameters and statistical expected error analysis to set the actual pressure gradient test parameters within an acceptable range of reliability. The method and system may account for one or more fluids within a formation and may also perform fluid contact analysis as part of planning the overall pressure gradient test. The method and system also include performing the planned pressure gradient test and comparing the measured data and statistical measured data error analysis with statistical expected error analysis of the measured data. The method and system may also include the graphical display of both the expected and measured data to optimize the pressure gradient analysis and the pressure gradient test procedure.

Method and system for statistical pressure gradient and fluid contact analysis

What We Have Learned from 29 Years of Well Testing in the Limoncocha Field: An Approach to Data Management, QA/QC, Interpretation, and Applications

When distributed pressure measurements are made with an RFT survey in a new well in a developed reservoir in many cases a near linear pressuredepth relation is observed. In some zones vertical pressure equilibrium is evident while in others the measured profile does not correspond to the hydrostatic gradient of the in-situ fluid because of viscous effects associated with a vertical flow component. The direct demonstration of the existence of, or deviation from, vertical pressure equilibrium gives valuable information on reservoir behaviour. The use of pressure gradient data in reservoir zonation and performance analysis through mathematical models is considered. Simplified models of differential depletion show how vertical flows in the reservoir may be inferred from production logging measurements in the wells. With this information the observed pressure profiles may be interpreted for the effective vertical permeability of barriers and tight zones. In the case where the well penetrates a zone containing two mobile fluids the theory of countercurrent gravity segregation is used to show how the measured gradient can correspond to the hydrostatic gradient of either fluid depending on the mobility ratio, or to an intermediate case. The difference between vertical pressure equilibrium in single-phase flow and vertical saturation equilibriummore » in two-phase flow is discussed. Permeability estimates from the buildup associated with each pressure test are used as a quality control parameter for the pressure measurements. The stochastic nature of the pressure observations is demonstrated and the minimum interval over which a pressure gradient can be determined within a given error bound is considered.« less

Luis Ayestaran

Papers

The Interpretation of Vertical Pressure Gradients Measured at Observation Wells in Developed Reservoirs