This case study analyzes formation damage at an oil field in Casanare, Colombia, where production declined due to contaminants. Remediation techniques like acid stimulation and hydraulic fracturing were implemented to restore permeability and enhance oil flow. The study also highlights various mechanisms of formation damage, including natural and induced causes, and provides insights into the operational factors affecting well productivity.

1. Abstract This case study examines the formation damage that occurred in an oil field located in
the Casanare region of Colombia. The oil field had been producing oil for several years, but the
operators noticed a significant decline in production rates. The investigation revealed that the
well was suffering from severe formation damage, which was caused by the accumulation of
drilling fluids and other contaminants in the reservoir. To address the formation damage, the
operators implemented a variety of remediation techniques, including acid stimulation, matrix
acidizing, and hydraulic fracturing. These techniques were designed to dissolve the contaminants
in the reservoir and increase the permeability of the formation, allowing oil to flow more easily
to the wellbore and to the understanding of formation damage mechanisms. The Ruba field is
one of the largest oil fields in Colombia and has been in production since the 1980 s. The oil
extracted from the Ruba field is a heavy crude oil, which requires more advanced refining
techniques to produce high-quality fuels. The Ruba field is operated by several major oil
companies, including Ecopetrol, the national oil company of Colombia. The concept of skin and
formation damage play a vital role in productivity of an oil well. The effect of formation damage
zone on the well flowing pressure was introduced to the original solution of diffusivity equation.
Formation damage reduces the well production. Skin defines as the area of reduced permeability
near the wellbore due to the invasion of drilling fluid into the reservoir rock. Classifying damage
requires a lot of work to determine correctly the main reason of it. In general, fluids can interact
with reservoir rock and cause formation damage that impedes hydrocarbon production. Tight
sandstone reservoir with well-developed natural fractures has a complex pore structure where
pores and pore throats have a wide range of diameters; formation damage in such type of
reservoir can be complicated and severe. Reservoir rock samples with a wide range of fracture
widths are tested through a several step core flood platform, where formation damage caused by
the drilling or fracturing fluid, where any unintentional fluid impedance in or out of a wellbore is
referred to as damage to formation. This general definition includes the flow restriction caused
by reduced permeability in the near wellbore region. Formation damage Description and
classification: The history of damage removal is a process that begins with the identification of
the issue. This usually involves looking through the various sources of information related to the
well, such as drilling records, completion designs, and operator experiments. The desired
purpose is to identify the causes of the formation damage and how it could be fixed. Where the
types of formation damage location of damage extent and screening of damage, and effect of
damage on well production or injection. Well development and reservoir exploitation practices.
Positive skin can attribute to the formation damage once mechanical pseudo skin effects are
identified. Formation damage is classified mainly as cither natural or induced by the mechanism
of its creation. 1. Natural damage: is mainly caused by the production of fluid in the reservoir 2.
Induced damages: are the result of an extemal operation that was performed on the well such as a
drilling, well completion, repair, stimulation treatment or injection operation. - Mechanical
mechanisms Fines migration: Buildup of fine particles, particularly in sandstone reservoirs, can
significantly reduce well productivity. See Formation damage from fines migration. Phase
trapping: a kind of mechanical formation damage that attacks the effective permeability, it can
occur when water-based well bore fluids come into contact with a formation which exhibits sub-
irreducible initial water saturation. Clay-particle swelling or dispersion: This is an inherent
problem in sandstone that contains watersensitive clays. When a fresh-water filtrate invades the
reservoir rock, it will cause the clay to swell and thus reduce or totally block the throat areas.
Scales: are water-soluble chemicals that precipitate out of solution in response to changes in

2. conditions or the mixing of incompatible waters. They can be present in the tubing, perforations
and formation. Organic Deposits: Organic deposits are heavy hydrocarbons (paraffin or
asphaltenes) that precipitate as the pressure or temperature is reduced. This is a form of
distillation. They are typically located in the tubing. perforations, or formation. - Chemical
mechanisms Rock fluid interaction: the reaction between the rock and the fluid may change the
chemical composition of the material which results in reduction in the permeability by plugging
the throat of the path Fluid/ fluid interaction: the interaction between the drilling fluid and the
formation fluid may impair the permeability of reservoir rocks, thereby reducing the natural
productivity of reservoirs. Over half of the reserves are found in Mirador Fm sandstones from the
Late Eocene, which was deposited in fluvial and shallow marine environments. Fluvial and
shallow marine Paleocene Barco Fm sandstones, as well as the shallow marine Campanian
Upper Guadalupe Sandstone Fm, are other deeper reservoirs. Ruba has a low porosity level, with
an average of 9% in the Mirador Fm. However, because the reservoirs are pure quartz cemented
quartz arenites with no permeability reducing antigenic clays or carbonate cement, good
permeability is maintained. The exceptional deliverability ( > 12 , 000 BOPD) of Ruba wells is
due to matrix permeability, not fracture permeability, according to core and well test research.
Ruba hydrocarbon phases occur in a critical point condition where they are nearly miscible.
Reinjection of generated gas is expected to result in very high liquids recoveries, according to the
analysis. To maintain reservoir pressure and evaporate leftover liquids, the field will be
developed by reinjecting generated gas. There are considerable amounts of hydrocarbon liquids
and large amounts of gas in the field. Up to this point, five data sources have been utilized to
assess the potential for well productivity. These include core analysis, open hole log data, drill-
stem test results, long-term test product performance, and technical service laboratory programs.
This research concentrates on examining the key phases involved in the well process that are
recognized to affect mechanical skin damage and resulting well productivity. The analyzed
phases include conceptual planning, reservoir mud systems, wellbore constraints, mud losses,
hardware constraints, perforating parameters, kill pill designs, and completion brines. Ruba field
has undergone 16 drill stem tests in the past two years, which are all deemed valid for analyzing
and computing mechanical damage to the skin. A majority of the gathered data up to this point
that indicates high levels of mechanical skin damage ( Sd > + 10 ) can be attributed to a well-
known operational issue. problem and/or constraint encountered during the operations (7 out of 8
DSTs). On a hygraded basis, the remaining data set ( 9 out of 16 DSTs) was evaluated.
Mechanical skin damage trends have been linked to operational parameters that affect well
productivity and flow efficiency. These patterns were then used to detect putative formation-
damaging phases and operations throughout the drilling process. The magnitudes of skin damage
have been used to define forecasts for well count and material procurement requirements based
on risk projected well productivities.