On Some Chemico-Mineralogical Transformations in a Petroleum Reservoir Exploited by In-situ Combustion

Abstract

In-situ combustion is a thermal recovery technique in which a part of the heavy oil in place is burnt to generate heat. This heat brings about a reduction in viscosity of the crude oil to lead to the improvement of the mobility and hence oil production rate and recovery. Typical combustion front moves slow (some cm/day) through reservoir matrix (pores) by consuming the fuel as it moves ahead. The combustion zone is often a few centimeters in thickness and it has a temperature up to 700-800oC. The hydrothermal conditions that occur in front of and behind the combustion zone may generate chemico-mineralogical transformations following or not from a new minerals forming. In the paper the authors emphasize for the first time calcium silicates hydrate forming in the matrix of siliciclastic rocks from oil reservoirs exploited by in-situ combustion.

Half a century of continuous oil production by in-situ combustion in Romania – case study Suplacu de Barcau field

“…It also requires attention from engineers and is less flexible and error-prone than steam. [1,[6][7][8][9][10][11][12][13][14][15] In-situ combustion (ISC) or fire-flooding is one of the oldest thermal oil recovery designed and patented in 1920 in U.S. [8,10]. ISC has proved as an efficient thermal method for heavy oil recovery which use the heat generated in the reservoir by burning a part of the heavy oil in order to decrease the crude oil viscosity improving the oil mobility and hence oil production and recovery.…”

“…The coke burning is supported by injecting air or an oxygen rich gas into the reservoir. [1,[6][7][8][9][10][11][12] According to the direction of injected air and combustion front there are two types of ISC: "forward combustionˮ if the air and combustion front are moving in the same direction, and "reverse combustionˮ if the injected air and the combustion front are countercurrent. Forward combustion can be divided into "dry forward combustionˮ (in the oil reservoir is injected only air to support the combustion) and "wet forward combustionˮ (in the oil reservoirs, air and water are co-injected into the formation through the injection well).…”

“…As intercalations were encountered clayey sands, polymictic sands, marlstones, greywackes, subgreywackes and microconglomerates. [4,[10][11][12][18][19][20] More details on the reservoir parameters are presented in the table 1.…”

“…Finally G. Branoiu (2007) in his doctoral thesis [11], and subsequently [4,12], performed a complex geological study consisting of mineralogical investigations by optical microscopy, X-rays diffraction and thermal analysis (thermogravimetric and thermodifferential analysis) on the rock samples collected from the burned area of the Suplacu de Barcau oil field. In the mentioned research it is shown that the reservoir rocks of the Suplacu de Barcau oil field have suffered a variable thermal regime with temperatures in the range 150-500ºC, which is proved by the mineralogical transformations and the exothermic/endothermic transformations observed in the rock samples studied.…”

“…Investigations by X-rays diffraction and optical microscopy performed by G. Branoiu [4,11,12] showed significant mineralogical transformations consisting in decreasing of the clay minerals content, formation of new minerals (calcium silicates hydrated and tobermorite minerals) and also grain size changes in the burned samples collected in the wells spudded in the burned area of the reservoir (K8, K20, K30, and K40). Decreasing of the clay minerals content and grain size changes have influence on the physical rock parameters modifying the porosity and the permeability and subsequently influencing the oil production rate in the reservoir.…”