Well Testing and Pressure Transient Analysis Flashcards
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Read the first 7 Well Testing and Pressure Transient Analysis flashcards as text
During a buildup test, the Horner plot is constructed by plotting shut-in bottomhole pressure versus the Horner time ratio. What does a slope of 'm' on this plot represent?
Answer: Formation permeability-thickness product (kh)
The slope 'm' on a Horner plot is directly related to the permeability-thickness product (kh) via the equation m = 162.6 qBμ / kh, allowing calculation of formation flow capacity.
In pressure transient analysis, what does a positive skin factor (S > 0) indicate about the wellbore condition?
Answer: Near-wellbore damage reducing effective permeability
A positive skin factor indicates near-wellbore damage (e.g., from drilling mud invasion or scale), which creates an additional pressure drop and reduces well productivity.
Which flow regime appears as a half-slope straight line (slope = 0.5) on a log-log plot of pressure derivative during a pressure transient test?
Answer: Linear flow
Linear flow, which occurs in hydraulically fractured wells or elongated reservoirs, produces a half-unit slope (0.5) on the log-log pressure derivative plot.
What is the primary purpose of performing a drawdown test rather than a buildup test in well testing?
Answer: To evaluate productivity without sacrificing production time by shutting in
A drawdown test acquires pressure transient data while the well flows, avoiding the production loss associated with a buildup test shut-in period.
In well testing, 'wellbore storage' (afterflow) distorts early-time pressure data. What causes wellbore storage in a producing oil well?
Answer: Fluid expansion or compression within the wellbore volume after shut-in or opening
Wellbore storage occurs because the wellbore volume contains compressible fluid; after shut-in, continued influx from this volume (afterflow) or fluid compression masks the true reservoir response.
The dimensionless wellbore storage coefficient (CD) accounts for afterflow effects in pressure transient analysis. Which well characteristic most directly increases CD?
Answer: Larger wellbore volume (e.g., larger casing ID or deeper well)
CD is proportional to the wellbore volume (C = Vwb × ct); a larger casing inner diameter or longer wellbore increases the storage volume, raising CD.
On a pressure derivative plot (Bourdet derivative), radial flow is identified by what signature?
Answer: A flat (horizontal) straight line
Radial flow produces a constant (flat, horizontal) pressure derivative on a log-log plot, making it the hallmark diagnostic for the infinite-acting radial flow regime.