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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). Expand | | |||||
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Fig. 1. Production/Injection History |
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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).
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
Radial Deconvolution Deconvolution ( Hint
- Pressure response of the well to its unit rate production in absence of other wells (also called Diagonal Self-Response or Drawdown Transient Response or
Hint 0 DTR1 Diagonal Transient Response )2 DTR - Pressure response of the well to offset well unit rate production in absence of other wells (also called Cross-well Transient Response or
Hint 0 CTR1 Cross-well transient response )2 CTR
A group of
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The main difference between between RDCV and single-well deconvolution (SDCV ) is that it takes into account offset wells impact on tested well pressure.
Only rates are taken into account for offset wells in RDCV.
In case a group of tested wells have mulitple pressue gauge installations one may wish to deconvolve the unit-rate transient responses using all of the pressure data which is called Cross-well deconvolution (
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The main advantage of
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The intervals between two wells with pressure gauge instaltions installations results in two transient response: first well onto the second well and revers.
This may indicate anisotropy of pressure propagation in counter directions and shed the light on the resevroir physics between these wells.
Once all possible DTR/CTR are deconvolved one can perform a conventional type-curve analysis for each well, defining the type and distance to the boundary, estimating skin, transmissibility and diffusivity around each well.
Unlike routine numericial fitting, where
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Main benefits of Hint
- Reconstruction of formation pressure history
- Rate corrections for random mistake
- The ability to get transient responses without initial knowledge of reservoir geometry
Main disadvantages of Hint
- Uncertainty in DTR/CTR, in case of uneventfull production history or synchronized correlated flow variation of two (or more) wells
- Error Uncertainty in DTR/CTR is increasing with the number of wells in the test
Sample
Sample #1 – RDCV
На рис. 2.1.2 представлена карта участка с тремя скважинами.
Синтетическая история работы добывающей скважины с простым поведением продуктивности.
Рис. 2.1.4. P1. Сравнение полученной истории дебитов и давления с исходными
Пример #2 – КДКВ
На Рис. 2.1.5 представлена карта участка с тремя скважинами.
Рис. 2.1.5. Синтетическая история работы добывающей скважины с простым поведением продуктивности
Рис. 2.1.7. Влияние скважины P2 на скважину P1
Рис. 2.1.9. Скв. Р2. Сравнение мультискважинной деконволюции и односкважинной деконволюции
На Рис. 2.1.15 приведена история дебитов и давлений по всем скважинам.
Рис. 2.1.15. P1. Сравнение полученной истории дебитов и давления с исходными
See also
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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Production Analysis (PA) / Pressure Deconvolution
[ MDCV @model ]
[ RDCV ][ RDCV @model ][ RDCV @sample ]
[ XDCV ][ XDCV @model ][ XDCV @sample ]
[ Multiwell Retrospective Testing (MRT) ]