Near Wellbore Stimulation

I believe there are many methods and processes to stimulate reservoir near wellbore. Among many popular methods (acidizing and fracturing), microbial stimulation and heat-vibration are still unpopular. Usually, the operator tries to avoid these methods since it is almost impossible to control the processes behind casing.

1. MICROBIAL STIMULATION

Bacteria can live in harsh condition such as in oil reservoir. Bacteria have very simple cellular structure (FIGURE 1)that helps it to stay dormant in reservoir pore. By improving the environment condition, bacteria can “wake-up” from dormant state to living micro-organism.  In very satisfaction environment, bacteria can grow by cell division and double in number as quickly as 9.8 minutes. Dormant anaerobic bacteria in the reservoir will stay dormant in the produced water. By sampling the water and analyzing in the lab, the bacteria can be identified and then the resource substances can be formulated to grow the bacteria. If there are no suitable bacteria in the reservoir to disclog oil, bacteria that will living mutually with residence bacteria will be injected from surface within injected water along with nutrients.

FIGURE 1: Bacteria with simple cellular structure

Microbe has certain criteria to grow. Generally, microbe can live below 80 ᵒC and 2400 psi. Salinity and pH also affect the optimum condition to grow microbe.

The substances that will unclog the oil and make it more movable are bacteria secretion. The secretion acts similar to chemical surfactant that influences surface tension oil-water and oil-rock. In very favorable condition, bacteria will multiply faster and produce more secretion. Phosphate must be supplied as part of bacteria nutrition beside of oil. As one cell organism, optimum thermodynamic activity in the form of oxidizing – reducing reaction will promote faster multiplying. Anaerobic bacteria such as sulphate reducing bacteria (SRB), nitrate reducing bacteria (NRB), iron reducing bacteria (IRB) and acetogenic bacteria will act as electron donor while Nitrate that is supplied along with injected water will acts as electron acceptor. The inventor believe vitamins such as  B12, biotin, folic acid, nicotinic acid, aminobenzoic acid, calcium pantothenate, pyridoxine HCl, riboflavin , thiamine,thioctic acid will promote better condition for bacteria to multiply.

Anaerobic bacteria that eat oil are more favorable than that does not eat oil. By eating oil, nutrient supplied along with injected water will be less. The rate and concentration of nutrients and vitamins must be determined in the lab. The inventor suggests the rate between 0.1 and 15 m/day and concentration between 1 and 1000 m g/l. The inventor also specifically avoids the use of oxygen.

2. HEAT-VIBRATION STIMULATION

Reacting two chemical substances in the reservoir is the idea. The reaction will produce micro-explosion (vibration) and heat. The chemical substances must endure at reservoir P/T before reaction. Spacer such as water, brine or carbon tetrachloride, is injected between chemical substances to avoid premature reactions.

The main chemical substance in the invention is pentaethylene hexamine -3CO (PEH-3CO, FIGURE 2). PEH-3CO (polymer) reacted with acid will produce micro-explosion, heat and CO2. The following is the stoichiometry of PEH-3CO / acid system:

PEH-3CO + nHX (acid) —-> PEH Hn + Xn- + 3CO2 + heat

FIGURE 2: PEH-3CO

Gas CO2 will increase pressure. Heat will decrease oil viscosity and vibration of micro-explosion will release trapped oil. Overall, the stimulation will increase oil recovery.

The vibration intensity and duration of micro-explosion can be controlled by the type and structure of the chemical substances used. The type and structure of the chemical substances must be evaluated in the lab. Compatibility check must be run to avoid precipitation in the reservoir due to negative ion Xn- since formation water contains several salts.

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