The paper describes advanced inter-well pressure interference testing used for 3D model calibration accounting for formation layering and rock compressibility in a mature Siberian waterflood field. The new interference test is based on pulse-code testing (PCT) and can scan inter-well zones without a longterm production shutdown, normally required for conventional pressure interference testing (PIT). There are numerous applications of this technique but this paper shows only two of them: Calibration of a geological model with respect to shale breaks by determining effective formation thickness by PCT and then its correlation with a production flow profile determined by Spectral Noise Logging and temperature modellingDetermination of rock compressibility distribution throughout a 3D simulation grid by estimating formation compressibility from PCT and correlating it with formation porosity from open-hole logs The importance of compressibility calibration cannot be overestimated because it defines the formation pressure response to the non-compensated or over-compensated withdrawals across the field and different pay zones. Conventional PIT can assess formation transmissibility and hydraulic diffusivity between wells. These two properties can be further converted to some basic 3D model inputs, for example effective formation thickness and compressibility, if permeability, SCAL, PVT and formation saturation are known. The main limitation of the conventional PIT is that it requires a receiving well to be shut-in to avoid contamination from production and that the pressure signal should not be contaminated by interference with other wells except the selected pulsing one. This limitation makes conventional PIT impractical for quantitative reservoir characterisation. PCT generates coded flow-rate pulses in one well and provides a mathematical technique to decode a pressure signal in receiving wells into components from each pulsing well. This allows running PCT in multiple working wells with pre-set rate variation without shutting down production and assessing several inter-well intervals in parallel. A one-month PCT described in this paper resulted in 5% production loss, while conventional PIT would need three months with 60% production loss and a high risk of failure due to pressure contamination from remote processes.
One of the common applications of Pressure Transient Analysis and Pressure Pulse Testing is the evaluation of formation permeability that is referred to as dynamic permeability and is then used to calibrate permeability distribution from a geological model before running full-field flow simulations. In practice, though, the correlation between permeability from pressure tests and that predicted from open-hole logs is often poor and does not provide consistent calibration because of many factors including poor core data, poor porosity-permeability, complex pressure transient responses and others. In many cases, inaccurate dynamic permeability values are due to misinterpretation of flowing thickness. In this paper, we demonstrate how Spectral Noise Logging can pick the boundaries of actual flow units and enable the accurate determination of effective thickness to substantially improve the correlation between dynamic and open-hole permeabilities.
Today, geological and hydrodynamic models are widely used for efficient development and monitoring of oil and gas fields. These models are designed to handle a wide range of tasks. Their reliability directly affects the quality of results and any uncertainties should, therefore, be minimised. The use of additional techniques can enhance the reliability and predictive ability of the models and minimise risks. This paper describes how integrating accurate description of flow geometry with reservoir properties and reservoir models to achieve this objective and, to generate a more reliable picture of the reservoir performance. The study included running HPT-PLT-SNL high precision logging tools, and covered a pilot area with five wells in a Cretaceous carbonate reservoir. The wells were completed in the lower and tighter Sub-reservoirs units F1 and F2 and the objective of this pilot is to identify the flow geometry in wells’ neighborhood, particularly identify channeling, fracture flows or other types of communication. The objective of the associated simulations and study is to correlate the acquired and interpreted data with those suggested by simulations and come up with consistent description of reservoir flow geometry within the pilot pattern. The most challenging point of this flooding campaign is the complexity of the reservoir in this area. The flooding pilot sets the targets for tight Sub-reservoir carbonates Unit F1 and Unit F2. It's important to know if the flow ensues exactly within these units and does not communicate with other reservoirs with better permeability.
A sandstone formation is showing accelerated production decline during the fully compensated waterflood development. The sporadic well tests suggested that liquid rate was following the non-uniform formation pressure decline, despite the full compensation of the offtakes. The paper presents a multiwell downhole pressure gauge deconvolution technique and associated study on the reasons of non-uniform area formation pressure decline and non-uniform injection water front propagation and resulted in recommendations which proved their efficiency after implementation.
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