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Qwestrum Engineering360 · Petroleum & Energy · Reservoir Engineering

Well Testing

Well testing extracts kh, skin, and boundary information from pressure transient response during drawdown and buildup operations.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.

Key formulas & points

Skim these first — then read the full notes below.

  • Build-up test shut-in pressure analysis
  • Permeability-thickness kh from slope
  • Boundary effects late time response

Topic details

Introduction

Dake and Ahmed both frame well testing as inverse analysis: measured pressure behavior is used to infer reservoir parameters. In university exams, semilog slope-based kh calculation is a high-frequency numerical.

Key relations & formulas

Formulas (Indian textbook notation)

  • Darcyradialflowq=kh(Pr−Pw)/(141.2μBln(rerw))Darcy radial flow q = kh(Pr-Pw)/(141.2\mu B ln(\frac{re}{rw}))

Formulas (Indian textbook notation)

  • transientΔpvslog(t)slopem=162.6qBμ(kh)transient \Delta p vs log(t) slope m = 162.\frac{6qB\mu}{(kh)}

Formulas (Indian textbook notation)

  • skinsfromwellboredamagestimulationskin s from wellbore \frac{damage}{stimulation}

Notation and sign conventions

Relation 1 —
Darcyradialflowq=khDarcy radial flow q = kh

Formulas (Indian textbook notation)

  • Darcyradialflowq=kh(Pr−Pw)/(141.2μBln(rerw))Darcy radial flow q = kh(Pr-Pw)/(141.2\mu B ln(\frac{re}{rw}))
Write this relation with symbols exactly as in Dake Reservoir Engineering — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
transientΔpvslogtransient \Delta p vs log

Formulas (Indian textbook notation)

  • transientΔpvslog(t)slopem=162.6qBμ(kh)transient \Delta p vs log(t) slope m = 162.\frac{6qB\mu}{(kh)}
Write this relation with symbols exactly as in Dake Reservoir Engineering — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
skinsfromwellboredamagestimulationskin s from wellbore \frac{damage}{stimulation}

Formulas (Indian textbook notation)

  • skinsfromwellboredamagestimulationskin s from wellbore \frac{damage}{stimulation}
Write this relation with symbols exactly as in Dake Reservoir Engineering — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Concept in depth

Early-time response may include wellbore storage, middle-time often shows radial flow, and late-time reflects boundaries or heterogeneity. By fitting pressure change against log time, engineers estimate transmissibility and skin factor, then decide stimulation, workover, or infill strategy.

Assumptions and validity limits

State assumptions explicitly before using any relation for well testing — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Reservoir Engineering viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

Step-by-step problem approach

1. Read the question and list given data with SI units (common in Reservoir Engineering papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to well testing.
4. Use equation 1:
Darcyradialflowq=khDarcy radial flow q = kh
.
5. Use equation 2:
transientΔpvslogtransient \Delta p vs log
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Applications & exam relevance

Well Testing appears in field development plans. In Indian petroleum curricula this topic is tested because it connects theory to reservoir behaviour and recovery.
GATE and semester exams often combine well testing with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use well testing?" — answer with a lab, mini-project, or plant visit example if possible.

Common mistakes in exams

Common mistakes are picking non-radial data for slope, forgetting unit constants in 141.2 or 162.6 forms, and reporting k instead of kh without thickness conversion.

Quick revision checklist

Before attempting well testing problems, confirm you can:
1. Build-up test shut-in pressure analysis
2. Permeability-thickness kh from slope
3. Boundary effects late time response
Revise the solved examples in Dake Reservoir Engineering — Standard reference and one previous-year GATE or university paper for this unit.

Worked examples

Try the problem first — open the solution when you are ready to check.

kh From Semilog Slope

Problem

During buildup interpretation, q = 500 STB/d, B = 1.2, mu = 2 cP, and slope m = 25 psi/log cycle. Estimate kh from m = 162.6 q B mu /(kh).

Solution

kh = 162.6 × 500 × 1.2 × 2 / 25 = 7804.8 md-ft (approx).

Conceptual check — Well Testing

Problem

In a Reservoir Engineering semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of well testing." What should a complete answer include?

📖 Standard books (India)

  • Dake Reservoir Engineering — Standard reference

    Read: Syllabus unit

    Referenced in Indian B.Tech syllabus

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