Because we try and keep Inflection Points relatively short; let’s assume, for the sake of brevity, we are discussing non-hazardous waste (we’ll have the hazardous material discussion in a future newsletter).
Let’s start with the solid, non-drilling “garbage”. Most of this type of material can be considered “trash”, and many contracts make the disposal of this part of the driller’s responsibility. For example, general packaging can be considered non-hazardous and the following items can fall into that category:
- Well screen and casing boxes, straps and shrink wrap.
- Drilling fluid containers – bags and jugs.
- Cement bags.
- Everyday trash – coffee cups, food wrappers.
- Wooden pallets.
Consultants, owners and drillers must be clear on who is responsible for the disposal of this material. Sites have various ways of dealing with trash, some have facilities (dumpsters, recycling, etc.) available, while others require the consultant and or driller to arrange for their own trash removal. And by the way, the hotel won’t take kindly to you filling their dumpster with cement bags, so these logistics should be worked out ahead of time.
Moving on to the solids from the drilling process (cuttings). A conservative estimate of this waste stream is normally fairly easy to calculate by estimating the volume of the borehole and adding about 25%. So a 1,000′ long horizontal bore, drilled at 9 7/8″ diameter will generate about 25 yards of material.
1,000 ft. x .53 cu.ft./lin.ft. x 1.25 ÷ 27 cu.ft./yd. = 24.5 cu.yd.
The above calculation is the estimated amount of solids generated from a borehole drilled mud rotary, utilizing a high quality drilling fluid cleaning/recycling system. The fluid cleaning system separates the solids from the mud and discharges “dry” material from the shale shaker and/or desilting/desanding cones off a chute into a roll off or transfer container. The cleaned drilling fluid is then recycled back down the borehole. Please note that this volume is based on the diameter of the hole, which is typically about 1.5 times the well screen and casing diameter. This is a conservative estimate of solids, as many times the horizontal borehole is not perfectly cleaned (some cuttings left in annular space), and in those cases, the solids generated may be as little as 0.75 times
the borehole volume.
The liquid fraction volume can get kind of fuzzy; this material consists of drilling mud (borehole volume and cleaning system tank volume), well development fluids, decon water and any contained storm water. Rather than try and figure each individual component, we normally estimate that the total fluids volume will be about three times the borehole amount. In the example above, the 1,000′ long, 9 7/8″ borehole contains roughly 4 gal./lin.ft. of borehole for a total of 4,000 gallons. So, we would estimate about 12,000 gallons of liquid waste. Is this method perfect? Absolutely not. However, it provides a basis for an estimate most of the time.
Therefore, for a 1,000′ long horizontal well installed utilizing a drilling fluids cleaning/recycling system we would generate about 25 cu.yds. of solids and 12,000 gallons of liquids. Where and how do we contain that material? Let’s not discuss that quite yet.
Over the last several years we have seen an increase in the use of horizontal wells at very small sites; think UST and dry cleaners. These sites are quite compact and the wells are normally short. In almost all of these types of well installations, the site is so congested we’re unable to use a drilling fluid cleaning system. In these cases we just use a “one pass” drilling method.
What does “one pass” mean? We mix our drilling fluid, pump it down the borehole, as the mud comes back the surface it goes straight into a waste container (not through a drilling fluid cleaning/recycling system). This liquid stream is a slurry that can contain between 5 % and 30% suspended solids. Note that when we use a one pass drilling method, the “3 time borehole volume” should actually be increased to “5 times the borehole volume”. When it comes to estimating the amount of slurry generated, it’s best to over predict and under produce. Keep in mind with this method we are not generating a separate solid waste stream, but a high solids slurry, and any slow drilling (i.e. rock or stiff soils) means more material may be generated.
Now how do we store the waste on site? The best container to use for the solids and liquids is a “water-tight” roll off container – IN GOOD CONDITION. Determine a location on site for the roll off(s), then call a supplier and tell them exactly what type of material is going to be stored. Insist they provide a new container if possible and request a polyethylene liner. The last thing we want as a project team is drilling fluid leaking from the roll off. While getting new, lined roll offs is a good plan to eliminate leaking, it may also be a good idea to have secondary containment around the containers. In fact, many sites require this step, and fortunately most experienced waste container providers will not only rent secondary containment, but also set it up during roll off