Borehole (Downhole or THP) pressure survey based on the pressure response to the periodic A specific implementation of Well Testing based on recording and interpretation of borehole (downhole or THP) pressure response to the pre-designed sequence of increasing and decreasing flow rate variations (also called "cycles" or "pulses" ).
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С некоторыми из вышеприведенных недостатков можно побороться с помощью метода фильтрационных волн давления (ФВД), которые являются модификацией классического метода ступенчатого гидропрослушивания. В этом случае, на возмущающей скважине меняют режим работы периодически (как правило, чередуя пуск и останов скважины), задавая порядка 3 – 5 циклов и используют приближенные аналитические оценки скин-фактора, гидропроводности и пьезопроводности. Разработаны аналитические методы, которые интерпретируют циклы с несимметричными плечами (время работы и время остановки скважины не одинаковы). Однако на практике очень редко когда удается выдержать циклирование с высокой точностью и в итоге аналитические методы не дают аккуратных оценок и требуется переход на численные методы интерпретации ФВД. Дальнейшим развитием идей ФВД является Импульсно-Кодовое Гидропрослушивание (ИКГ - Мультискважинное Импульсно-Кодовое Гидропрослушивание), которое представляет собой численное решение задачи выделения и моделирования отклика из зашумленного сигнала и существенно расширяет область применимости гидропрослушивания на практике. |
The usual practise is to create 3 - 5 pulses.
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- the same well where the flowrate is varying ( and in this case is called Self-Pulse Test)
or
- in the offset well (an in this case is called Pressure Pulse Interference Test)
at one or more wells (called "generators" or "pulsers") inducing pressure pulse propagation across the field.
The usual practice is to create 5 – 10 pulses.
It splits into two categories:
| Pressure Self-Pulse Test (SPT) | Pressure Pulse Interference Test (PIT) |
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The pressure response to rate variation are both recorded in the same well | The pressure response to rate variation is recorded in the offset wells |
Workflow
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| 1 | Designing flowrate variation pulse sequence for disturbing wells (also called generators) based on the field primary data |
| 2 | Field operations on suspending the downhole gauges (if PDG is not available) |
| 3 | Performing flowrate variations according to the PCT design |
| 4 | Retrieving the downhole gauges |
| 5 | Downloading the data from the downhole and surface gauges |
| 6 | Primary data processing (gauge syncronization and filtering) |
| 7 | Implementing pressure pulse-code decomposition (PCD) |
| 8 | Recognising the PTA type-library diffusion models for decomposed DTR/CTR and type-curve fitting them with analytical and/or numerical pressure diffusion models |
Data Processing
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In case of harmonic pressure In case of harmonic pulsations and sufficiently long pressure-rate delay and a simple diffusion model (single-bed homogeneous reservoir without boundary) the test data pressure response can be approximated by analytical model:
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q=q_0 \cdot \cos \left(\frac{2 \pi \, t}{T} \right) |
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p=p_0 \cdot \cos \left(\frac{2 \pi \, t}{T} + \delta \right) |
where
. In this case the pressure data at receiving wells are being detrended and then matched to analytical model.
In case of periodic but non-harmonic pulsations one can use top-hat Fourier filter to isolate the harmonic components from total response and then apply harmonic pulsations interpretation models.
In case of non-periodic pressure pulsations with pressure contamination caused by interference with routine production and maintenance field activity, the complexity of pressure variation at receiving end maybe very high and the concept of "cycles" may not apply at all.
In this case the actual pressure responses should be decoded from pressure data records at receiving well using specialised pressure pulse-code decomposition algorithms and then decomposed DTR/CTR is recongised PTA type-library diffusion models and matched by diffusion models.
This type of tests is called Pressure Pulse-Code Test but this approach is equally applicable to simple periodic pulsations.
Interpretation
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See Also
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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Well Testing / Pressure Testing / Cased-Hole Pressure Transient Test / Pressure Interference Test (PIT)
[ Well & Reservoir Surveillance ] [ Unit-rate transient response (UTR) ] [ Pressure Pulse Propagation ]
References
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\delta = \frac{\pi}{8} + \frac{L}{\sqrt{\chi \, T}} |
phase shift related to the pressure response delay to the flowrate variation
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p_0 = \frac{q_0}{\sigma} ... |
pressure response to the flowrate variation
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\sigma = \left< \frac{k}{\mu} \right> h |
transmissbility
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\chi = \left< \frac{k}{\mu} \right> \frac{1}{c_t \, \phi} |