Why does the screen casing sand retaining blockage occur?

Posted by BAOWI STEEL MANUFACTURING CO.,LTD on May 7th, 2024

Characteristics of sand retaining media and sources of clogging

The screen casing used for sand control in oil and gas wells mainly include wire-wound screens, slotted liners, metal wool sand filter pipes, resin quartz sand sand filter pipes, metal mesh (felt) sand filter pipes, precision composite microporous sand filter pipes, etc. There is a sand filter layer inside the sand filter pipe, which is the sand retaining medium. During the production process of mechanical screen sand control wells, the sand-retaining medium is easily clogged by mud, silty sand and other obstructions, causing the screen permeability to decrease and forming a new skin coefficient, thus causing the oil well production to decrease or even stop production. Although there are more than a dozen types of mechanical sand control screen media used, most of the sand retaining media are multi-layer filters, slotted gaps, metal wool, and granules. The sand-retaining medium is essentially a solid-phase multi-media with a certain pore throat size, permeability and porosity. Its permeability ensures sufficient fluid passing capacity, while the pore throat size determines its sand-retaining performance.

The blockage of sand-retaining media in sand control wells is mainly solid particles, and their main sources are:

①Fine sand from the formation, that is, the fine component in the sand produced from the formation:

②Clay mud, mainly clay minerals in formation cement;

③Solid phase pollutants during the drilling and completion process, such as drilling fluid solid particles, debris caused by perforation, etc.

④ Colloidal asphaltenes in crude oil

⑤ Organic scale and inorganic scale formed during the production process. Solid plugs provide the source of clogging, and the plugging process and degree of plugging are affected by factors such as the composition of solid plugs, oil well production, sand production rate, and crude oil viscosity.

The sorting bridge filling and blocking mechanism in the non-filling space.

For mechanical screen sand control, after construction, a mechanical screen is lowered into the oil layer in the well to block the formation sand produced from the formation, forming an annulus between the screen and the casing. There is no filling material in the annulus and the perforations. , called the non-filled zone.

After the oil well is put into production, the formation fluid carries solid particles (formation sand and plugs) and produces them. The solid particles will fill the non-filled zone outside the mechanical screen through a sorting bridge mechanism, forming a low permeability layer and causing blockage of the oil well. , reduce production.

The sorting bridge mechanism refers to the impact of formation sand and blockage on the sand control screen along with formation fluid production. In the early stages of production, some solid particles that are fine enough enter the screen tube sand-retaining medium (or are continuously discharged or blocked inside the sand-retaining medium), while solid particles with a particle size larger than the pore throat diameter or slit width of the sand-retaining medium cannot After entering the sand-retaining medium and being blocked outside the screen tube, the coarser particles accumulate to a certain thickness and form a new porous media sand-retaining layer, but its pore throat size is smaller. This porous medium with very small pore throats will block the finer formation sands. And so on until the space is completely filled. Extending from the screen tube to the outside, the size of the blocked particles becomes smaller and smaller, and their permeability becomes lower and lower, increasing flow resistance and causing a decrease in oil well production.

The internal bridge clogging mechanism of the sand-retaining medium refers to the irregularity and heterogeneity of the pores of the sand-retaining medium inside the sand-retaining porous medium when fine solid particles enter the sand-retaining porous medium, making it difficult for the incoming solid particles to be discharged, resulting in a reduction in the permeability of the mechanical screen. form a blockage. Whether it is the solid particles in the drilling fluid, the particles produced during the perforation process, and the fine sand in the formation, they will all have an impact on the permeability of the sand retaining medium. For mechanical sand control screens with high original permeability, the permeability damage will exceed 90% in case of severe blockage.

According to the above analysis, the clogging process and final clogging degree of the bridge within the screen sand retaining medium are directly related to factors such as the composition of the solid plug, oil well production, sand production rate, and crude oil viscosity.

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