Inverse problem to pressure convolution, performed as a fully or semi-automated search for initial pressure for every well and Unit-rate Transient Responses (UTR) for wells and cross-well intervals in order to fit the sandface pressure response (usually recalculated from PDG data using wellbore flow model for depth adjustment adjustment) to total sandface flow rate variation history (usually recalculated from daily allocations based on surface well tests, see Fig. 1). Basic concept
The basic element of deconvolution is the pressure Unit-rate Transient Response (UTR) which is a sandface pressure response to the total sandface unit-rate production (see Fig. 2). Image Added | Fig. 2. UTR output diagram from XDCV. The column wells showing pressure response to row wells. Diagonal elements are showing self-response DTRs. Non-diagonal elements showing cross-well response CTRs. |
Multiwell deconvolution (MDCV) specifies two types of UTR: Drawdown Transient Response (DTR) and Cross-well Transient Response (CTR). The Drawdown Transient Response (DTR) is the the imaginary sandface pressure response of a given well to its total sandface unit-rate production in absence of the other wellsunder condition that no other well is producing/injecting. It is equivalent to conventional Drawdown Test with sandface unit-rate production as if the well is not interfering with surrounding wells. The Cross-well Transient Response (CTR) is the sandface pressure response of a given well to the total sandface unit-rate production of the offset well in absence of the other wellswell under condition that no other well is producing/injecting.
It is equivalent to the Pressure Interference Test with the unit-rate production in disturbing well as if the receiving well is shut-in and no other well is producing/injecting.
Although the UTR may last the infinite time but in reservoir engineering practise the UTR is usually assumed to be captured when it develops a boundary-dominated Late Time Response (LTR). It should be noted that sometimes the duration of production history is too short to sense the geometrical boundary and UTR will not capture it in full or not see a boundary at all. The true UTRs are also difficult to acquire in practise as most wells are noticeably interferring during at long-term scales. The exception is the remote well or the well draining an isolated compartment. This defines the application of MDCV which pretends to decipher the UTR from BHP and Production/Injection History. The pressure convolution principle itself has some limitations and may not be adequate for some practical cases. For example, changing reservoir conditions, high compressibility – everything which breaks linearity of diffusion equations. There are some workarounds on these cases but the best practice is to check the validity of pressure convolution (and therefore the applicability of MDCV) on the simple synthetic 2-well Dynamic Flow Model (DFM) with the typical for the given case reservoir-fluid-production conditions.
MDCV can be performed in two options: Radial Deconvolution ( Hint |
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