ASP Flooding

ASP flooding is a Chemical Enhanced Oil Recovery method where Alkali, Surfactant and Polymers are injected either in a given sequence or all together. The three chemicals have different effects. Often they interact with reservoir fluids (oil & water), rock minerals and among themselves to enhance oil recovery. In this article, we will explore these effects.

Effects of Alkali:
Alkali such as Caustic Soda (Na2CO3) are added to the chemical cocktail. It has two primary impact:
(a) Alkali reacts with the in-situ "Petro-Acids" and produces "Soap", a kind of surfactant. It compliments the surfactant requirement.
(b) Alkali competes for the absorption sites along with polymer and surfactant.
(c) Alkali causes 'emulsification' which improves sweep efficiency.
PLUS
(d) Oil Entrainment Effect
(e) Bubble Entrapment Effect
(f) Wettability Reserval

Effects of Surfactant:
Surfactant primarily works and IFT reducer. It loosen up the oil particles attached to the rock surfaces and thus assist move them closer to  the producing well. The effect is usually quantified using "Capillary Number", defined by:

          Nc = uμ / σ

where,
          u = displacing fluid velocity
          μ = displacing fluid viscosity
          σ = Inter-Facial Tension (IFT)

As Capillary No. increases, more oil droplets get detached from the rock surfaces and move towards the producers. In other words, it reduces the Irreducible Water Saturation (S_wirr).

Effects of Polymer:

• Polymer helps in improving the sweep efficiency of the injected chemical by mobility control.
• Due to "ViscoElastic" property, polymer flooding helps push/pull oil droplets from dead-end pores.
• Another, often ignored positive impact is the favorable economics compared to water injection. For the same effect, less amount of pore volume need to be injected.

The Synergies and Interactions of ASP:
When the three types of chemicals, namely Alkali, Surfactant and Polymer are injected "together", an increased oil recovery is observed. It is probably due to the advantage obtained due to the synergies and interactions between the said chemicals. These effects can be summarized as follows:
1. Alkali competes with absorption sites and hence reduces polymer and surfactant absorption, hence their requirements.
2. Alkali reacts with acidic crude oil and generate soap, called "petro-soap". This soap has low optimum salinity whereas injected synthetic surfactant has higher optimum salinity. As a result, the mixture of petro-soap and synthetic surfactant has a wider range of optimum salinity where IFT is low.
3. Emulsion improves sweep efficiency as the small bubble blocks the wider pore throats and forces the displacing fluid to enter the narrower pore throats. Petro-soap and surfactant make emulsion stable due to reduced IFT. Polymer may also help to stabilize emulsions owning to its high viscosity to reduced coalescence.
4. Addition of polymer improves sweep efficiency of the entire chemical slug, enabling more oil bearing zone exposed to surfactant and alkali.

Abbreviations

OAPL = Open Acreage License Policy HELP = Hydrocarbon Exploration and Licensing Policy NELP = New Exploration Licensing Policy NDR = National Data Repository

Black Oil vs Compositional Modeling

We often hear the Reservoir Engineers talking about Black-Oil model and Compositional Model. What are these? How do they compare? 

All these are different fluid model or the part of numerical simulation model that handles how the fluids, that is, oil, water, gas and any other substances would behave at different pressure and temperature.

Black Oil model is relatively simpler model with only three fluids - oil, water and gas. 

An extended version of Black-Oil model, called Extended Black Oil model takes are of volatile oil in gas and dissolved gas in oil.

A Compositional Model  on the other, tracks any number of components the fluid might actually has - like different hydrocarbons (C1, C2, C3, C4. C5, C6, C7,... etc), H2S, CO2, Water etc. These models are complex and takes lot more computing time than Black-Oil models.  

Brain Deposit !!

In the recent visit to the USA while addressing a large crowd of the Indian diaspora of the Silicon Valley, Indian Prime Minister Sri Narendra Modi mentioned an interesting term - "Brain Deposit". For him, the flow of talents from India to other countries is not "Brain Drain", rather "Brain Deposit", that he hopes that one day will return to "Mother India" with interest, i.e. with enhanced expertise. That`s what he calls "Brain Gain With Interest". According to him, that day is perhaps now or in the very near future.

Does it apply only to the IT sector or to our Oil&Gas sector as well? The Indian E&P companies including Oil India and ONGCL have experienced "Brain Drain" for quite a long time. These companies groomed talents in various fields like geosciences, reservoir engineering, production engineering, drilling etc from the very nascent stage. They hire fresh graduates, often with degrees with no direct relevance to the industry and spends time, money and man-hours to train them. After working and gaining experience for few years, many of them leave the company and the country in search of better opportunities. The time, money and man-hours spent apparently goes down the drain. The expertise and skills imparted by the Indian companies are utilized later by the foreign companies. Are these "Brain Drain"  or "Deposit" ?  

Volumetric Method of Reserves Estimation

The volumetric method of reservoir is a very simple and yet elegant mathematical tool that gives a fairly accurate idea about the volume of hydrocarbons in the reservoir. Its accuracy depends upon a correct estimation of certain physical properties of the reservoir viz. Porosity , Reservoir thickness .

In the simplest mathematical terms , the volume is determined as 

Where , V is the volume of the hydrocarbon in reservoir
              A is the area over which the reservoir is spread
              h is the thickness of the reservoir
              phi is the reservoir porosity
              Swc is the connate water saturation
              Bo is the formation volume factor