A Real-Field Experience Related to an Oil Well Testing
We conducted a well test using two choke sizes. At choke 16/64″, there was no water production, and the oil surface samples were dark green in color. The measured flow rates were unstable, varying each time and showing unusual production. At choke 24/64″, surface samples showed BS&W ranging from 0% to 90%, which was very strange! The color of the fluid varied from dark green to light brown. The salinity of the water was about 300,000 ppm and we thought there was a leak from the Gachsaran formation.
A PLT was requested. The PLT tool could not enter the open hole section, but water production from the open hole was confirmed.
Now I want to apply a proper problem-solving method to solve this issue.
To resolve this complex yet common well behavior issue, we’ll apply a structured, step-by-step problem-solving algorithm based on engineering principles and rapid well diagnostics.
🎯 Main Problem: In this section, you should tell what issues you have doubts and questions about and raise those as problems:
- The well shows unpredictable water production behavior, with water cut ranging from 0% to 90% at different choke sizes
- Unusual fluid colors
- Unstable production rates
Step 1: Define the Problem Clearly
- At choke 16/64″, no water was produced.
- At choke 24/64″, water cut varied from 0% to 90%.
- Water salinity = 300,000 ppm → suggests possible Gachsaran water leakage.
- PLT couldn’t fully enter the open hole, but water production from that zone was confirmed.
- Production is unstable and flow rates are inconsistent.
Step 2: Gather Data
We must organize all available data in a structured way:
- Well Name? (to be specified)
- Previous tests?
- Completion type?
- Formation position (Gachsaran & productive zone?)
- Wellhead pressure?
- Production rate trend (Unstable / stabilized)
- Oil color (Dark green / light brown)
- Water color (Clear? Muddy? Any odor?)
- Water salinity (300,000 ppm)
- PLT results (Tool blocked; water flow from open hole confirmed)
- Pproduction history of the well during drilling, completion and workover
Step 3: Identify Potential Root Causes (RCA)
Possible Scenarios:
- Leakage from the Gachsaran formation through casing (Liner lap) or a natural fracture.
- Breakthrough from a water-bearing zone in the open hole (potential channeling or unseen aquifer).
- Emulsion formation or contamination from drilling fluid → leading to color change.
- Scale buildup or plugging, causing variable flow rates.
- Sampling error
Step 4: Plan Diagnostic Tests
- Repeat PLT with better tools (Pinpoint exact water entry zone)
- Isotope or salinity comparison of produced water (Identify source: Gachsaran vs aquifer vs contamination)
- Plot water cut vs choke size (Identify drawdown-related behavior)
- Emulsion/contamination test (Verify fluid integrity)
- Downhole camera, if feasible (Visually identify flow paths or damage)
Step 5: Analyze Patterns
Use rule-based logic to narrow down root causes:
- If water appears only at high chokes → likely breakthrough at high drawdown.
- If PLT confirms specific water entry zone → check for zonal isolation issues.
- If salinity is extremely high → casing leak or formation communication.
- If color and salinity change erratically → possible emulsion or contamination.
- If rates are unstable → check for scale or fluctuating flow paths.
Step 6: Recommend Action Plan
- Control drawdown by keeping choke size small to avoid sudden water entry.
- Repeat PLT to identify active water-producing intervals.
- Analyze water chemistry to differentiate between formation water and leakage.
- If casing leak is suspected → run CBL or RBT or HPT/SNL to check well integrity.
- If open hole zone is the issue → consider chemical/mechanical shutoff options.
🧠 Well Checkup Platform’s Rule-Based Engine
If you have a similar challenge to this, we created a checklist for erratic water behavior diagnosis and added this behavior type to the Well Checkup platform’s rule-based engine.
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