Field Operations

Chemical Treating on the Lease: Corrosion, Scale and Bacteria Control

Chemicals are the cheapest tools on a lease, and the easiest to use wrong. The right dose keeps a well open and producing; the wrong chemical, rate, or a skipped treatment shows up later as a parted rod, a scaled pump, or a line that will not flow. Treating is routine work, but only when it is done on schedule and checked against results.

What treating is for

Produced fluids are hostile. Formation water carries dissolved salts, carbon dioxide, and sometimes hydrogen sulfide, and that mix eats steel. Scale forms when pressure and temperature drop as fluid moves up the well and minerals that were dissolved downhole come out of solution, coating the pipe, pump, and perforations. Paraffin drops out of crude as it cools. Bacteria grow in produced water and in dead legs of lines. Oil and water, churned by a pump, make emulsions that will not break in the heater treater.

Each problem has its own chemical. Corrosion inhibitors film the metal so water cannot reach it. Scale inhibitors keep minerals dissolved. Paraffin solvents and crystal modifiers handle wax. Biocides knock down bacteria. Demulsifiers break oil and water apart so the treater can do its job. None of them replaces good mechanical practice, like routine wellhead maintenance; they are the second line of defense.

How programs run

Most lease treating is one of three methods. Batch treatment dumps a measured volume of chemical into the annulus, often cut with water or oil, and lets it fall to the bottom of the well. It is produced back out over days or weeks, coating the tubing and pump along the way. It is the standard method on rod-pumped wells and costs nothing in equipment: just a barrel and a man on the ground.

Continuous injection runs a small chemical pump at the wellhead or on the flowline, pushing inhibitor into the stream at a few quarts or gallons a day. The pump needs a daily check: the sight glass, the stroke rate, and the tank level tell whether chemical is actually going in.

Flowlines get treated too. Chemical injected at the wellhead travels down the line and protects it; on long lines or corrosive water, operators batch-treat the line itself or add a second injection point. Whatever the method, the work is only as good as the log: date, chemical, volume, and who did it. Treatment schedules and the readings that prove they work are the kind of records software like OpsFlo keeps with the well file.

Treating down the annulus also means watching the annulus: a well with sustained casing pressure has to be handled on its own terms before any chemical goes down the backside.

Watching the results

Treating is a bet you can check. The standard check is the corrosion coupon: a weighed strip of steel set in the flow, pulled on schedule, cleaned, and weighed again. The weight lost between pulls, divided by time in service, is the corrosion rate, compared against the target the operator set.

Water analysis is the second check. Iron counts in produced water climb when corrosion is active, because pipe iron is ending up in the water. Sulfate counts fall when sulfate-reducing bacteria are at work, and culture bottles or ATP tests show the bug population directly. Operators sample on a set schedule and watch the trend.

Flow and pressure trends are the third check. A well that holds its production and pressures is probably treated well. Tubing pressure that keeps creeping up, a pump that keeps getting scale, or a treater that keeps making rag layer all point to a treating problem. When the numbers move the wrong way, the answer may be a different chemical, rate, or method, not more of the same.

Pipelines: the corrosion control rules

When the treated stream leaves the lease into a regulated gas pipeline, corrosion control stops being good practice and becomes a rule. Pipelines operated under 49 CFR Part 192 must have a corrosion control program, and the internal corrosion rules in Subpart I require the operator to determine whether the gas is corrosive, monitor for internal corrosion, and control it, with inhibitors where monitoring shows they are needed. The specific requirements sit in 49 CFR 192.476.

That rule does not reach the lease pumper, but it reaches the operator taking delivery at the sales meter. Corrosion in a gathering line usually starts in the water the lease produced, so the program that protects the well also protects the line. Pipeline operators want to see that the treating is real: records of chemical runs, coupon results, and water tests are the evidence, and the lease that keeps the paperwork can answer when they come.

Handling chemicals safely

Treating chemicals are concentrated, and the work starts before a drum is opened. Read the safety data sheet before the chemical gets to the lease, and read the label on the drum. The SDS names the hazards, the protective equipment, and the first aid response, and it travels with the chemical: no SDS on site, the drum stays shut.

Protective equipment is not optional at the barrel. Chemical-resistant gloves, safety glasses with side shields, and often a face shield and splash apron belong on the person handling the chemical, and boots and coveralls keep spills off skin. The PPE basics that apply across the lease apply double at the treating tank. Never mix chemicals blind: some combinations react, heat up, or give off gas, so nothing gets mixed until the SDS says it is compatible.

Spills are a when, not an if, so the site is set up for them. Chemical tanks sit in secondary containment, a diked area or double-walled tank that catches the contents if a tank or fitting fails, so chemical cannot reach the ground, the pit, or a waterway. Spill kits with absorbent pads, booms, and the right gloves are staged where the chemical is handled. The same thinking that governs SPCC plans at tank batteries applies at the treating skid.

Empty drums and leftover chemical are not trash. Rinsate and unusable product go to disposal routes the operator has set up; dumping chemical on the ground or down the pit is how a routine job becomes a reportable one. Treating works when the person doing it knows the chemical, wears the right gear, and keeps the paperwork.

Sources and further reading

• AMPP: Association for Materials Protection and Performance (corrosion resources)
• eCFR 49 CFR 192.476: Internal corrosion control of gas pipelines