TREATMENT OF DRILLING MUD WITH “PACS-T” ADDITIVE

TREATMENT OF DRILLING MUD WITH “PACS-T” ADDITIVE

Annaguly Deryaev

Candidate of Technical Sciences, Senior Researcher, Scientific Research Institute of Natural Gas of the State Concern “Turkmengaz”,

Turkmenistan, Ashgabat

ABSTRACT

inhibited fluids after long stops (for the period of geophysical surveys and others) restore the circulation of the fluid at intervals after lowering the drilling tool into the cased part of the wellbore (casing shoe). What causes the sedimentation stability of the solution for a long time and reduces the likelihood of sticking the drill string due to the retention of suspended particles of barite and cuttings.

Keywords: sludge, inhibitory additives, reagent, filtration property, viscosity, surfactant, dispersion, thickening.

Inhibited solutions have increased clay capacity, fixing properties of the filter cake which help to achieve an increase in the stability of the near-wellbore zone. Therefore, the solutions transferred to the inhibited system can withstand high values of fluid loss by 1.5-2.0 times in comparison with the required values laid down in the geological and technical order (GTO), and at the same time are able to maintain the stability of the wellbore for a long time.

One of the properties of inhibited solutions is the strength gain of the structure in time. Therefore, after long stops (for the period of geophysical surveys and others), the mud circulation is restored at intervals after the drilling tool is lowered into the cased part of the wellbore (casing shoe). That causes the sedimentation stability of the solution for a long time and reduces the likelihood of sticking the drill string due to the retention of particles of barite and cuttings.

While drilling in unstable deposits of clay rocks in the zone of moderate and elevated temperatures, it is necessary to use inhibited drilling fluids for successful accident- -free well drilling.

Known inhibited solutions, reflecting domestic and foreign experience in well drilling [1, 2]. NaCl, KC1, CaSO₄, CaCl₂ salts, silicates, fatty acid soaps, lime are used as inhibitory additives in these solutions. However, when they are used, the inhibition effect is lower, since inhibitors, as a rule, neutralize only one of the two lyophilic areas of the mosaic surface of clay particles: either along the planes - negatively charged areas, or along positively charged faces and fractures. Since clays are diphilic and strongly amphoteric, unilateral inhibition will be much less effective than multilateral inhibition.

There is a known method of processing a clay solution with a combined reagent [3], including, in mass. %: (as a supplier of inhibitory components) cement 10 - 25, clay 10-25, caustic soda 0.2 - 0.4, (viscosity reducer) sulfite-alcohol stillage (SAS) or its derivatives 4 - 8, water (the rest).

However, the inhibited system has disadvantages. The composition of the reagent is clay (10-25%), which increases the content of the clay phase in the solution up to 40-55%, causing an additional load on the clay capacity of the solution and the solution purification system. In addition, sulfite-alcohol stillage or its derivatives cause strong foaming, which is reflected in the parameters of the inhibited solution: the solution "swells", its volume increases, its density decreases and viscosity increases. The disadvantages also include a long preparation time of the inhibited reagent.

The closest in terms of essential features and the achieved result is the method of treating the drilling fluid with the inhibited complex additive " PACS" [3,4], including its introduction into the drilling fluid in the amount of 8-15% of the initial volume of the solution. The inhibited complex additive " PACS" contains, in mass%: (as a supplier of inhibitory components) Portland cement 10-12 and potassium chloride, viscosity reducers - lignosulfonates (SAS, CSAS, FCLS) 10-15, as a defoamer - a surfactant 1-2, caustic soda (NaOH) 4 - 5 and water.

However, the inhibited system has a drawback, when in the zone of moderate (+61°C to +100°C) and elevated (+101°C or more) temperatures, the mobility of the drilling fluid is lost and the protective properties of the reagents are reduced, which affect parameters of the inhibited solution: viscosity increases, structural-mechanical, rheological and filtration properties.

The technical objective of the invention is to increase the efficiency of inhibition and stability of the drilling fluid in the zone of moderate and elevated temperatures.

The solution of the technical problem is achieved by the fact that when performing a drilling mud treatment method, including the introduction of a complex inhibited additive " PACS" into the drilling mud, consisting of Portland cement, potassium chloride, caustic soda, lignosulfonates, a surface-active substance (surfactant) and water, in the composition of the additive additionally injected: sodium dichromate (Na₂Cr₂O₇) or potassium (K₂Cr₂O₇) in the following ratio of components, mass %:

Portland cement                                          -10 - 12

Potassium chloride                                     -10 - 15

Lignosulfonates                                          -10 - 15

Caustic soda                                               - 4 - 5

Sodium or potassium dichromate                - 3 - 4

Surfactant                                                  - 1 - 2

Water sea, technical, reservoir                     - the rest.

The specified composition is called a complex inhibited thermally stabilized additive “PACS-T” (Calcium-potassium-Aluminate Inhibited Solution - Thermally stabilized). It is a composition consisting of inhibitors, stabilizer, heat stabilizer, caustic soda, surfactant and water.

As a stabilizer and viscosity reducer, lignosulfonates are used - salts of lignosulfonic acids (SAS, CSAS, FCLS), which still have additional hydrophobizing power. However, lignosulfonates cause foaming in the drilling fluid and do not naturally degas.

Combined surfactants (XT-48) are nitrogenous surfactants in a mixture of block copolymers of polyoxyalkylenes - ethylene and propylene oxides, and is an active defoamer. The defoaming mechanism lies in the fact that XT-48 binds the hydrophobic part of the lignosulfonate molecules. In addition, due to the adsorption of XT-48 on clayey rocks, the adsorbed XT-48 molecules shield active sites on the clay surface, preventing their interaction with water.

The role of a heat stabilizer is performed by salts of chromic acid - sodium bichromate (Na₂Cr₂O₇) or potassium (K₂Cr₂O₇).

The role of inhibitors is performed by potassium chloride and alkaline hydrolysates of portland cements, which form acid-potassium chloride and acid-base hydrolysates with sodium or potassium dichromates, which prevent hydration, swelling and disintegration of clay rocks in the zone of moderate and elevated temperatures. An increase in the level of inhibition occurs due to the translation into a water-soluble state of potassium and calcium compounds present in potassium chloride and Portland cement - in the form of potassium and calcium monochromate.

Acid-base hydrolysates of portland cements contain water-soluble and insoluble compounds, the mineralogical composition of which includes:

tricalcium silicate - 58,0-62,0%; - 3СаО-SiO₂+Н₂О+К₂Сr₂О₇;

dicalcium silicate - 14,5-18,5%; - 2СаО-SiO₂+Н₂О+ К₂Сr₂О₇;;

tricalcium aluminate - 4,0-6,0% - Са₃Аl₂О₆-SiO₂+ Н₂О + К₂Сr₂О₇;

tetracalcium aluminoferrite - 13,0-15,0%; - Са₄(Аl₂О₆)(Fe₂O₅) +  Н₂О + К₂Сr₂О₇.

These water-soluble acidic compounds are in dissociated form and are effective anionic clay inhibitors.

Potassium acid chloride (KCl) enhances the inhibitory effect of the complex additive due to the unique property of the potassium ion. Potassium is not hydrated and, therefore, has a minimum size in the aquatic environment. This allows it to penetrate into the interplanar space of clays, preventing their hydration and swelling.

The set of essential features provides a new technical result. This is due to the fact that the developed system provides a multilateral, more effective inhibition of clay particles due to water-soluble acidic and alkaline hydrolysates of portland cement, containing both cationic and anionic forms of mineral inhibitors, enhanced by the inhibitory effect of potassium ions and chromic acid salts, capable of penetrating into the interpacket distance of clays, and hydrophobic action of combined surfactants based on their chemisorption on hydrophilic and hydrophobic exposed clay particles. This helps to obtain a combination of inhibitors: calcium, potassium, aluminate, silicate, polymineral. The anions and cations released as a result of acid and alkaline hydrolysis under the action of surfactants actively affect the state of the drilling fluid, the clay rocks that make up the walls of the wells, due to the drilling fluid filtrate, and the drilled clay rock itself. In addition, the complex surfactant in hydrocarbons completely degasses the foam and prevents its formation.

Various types of drilling fluids can be processed by the inhibited thermally stabilized complex additive “PACS-T”, including clay solution.

The inhibited system “PACS-T” (calcium-potassium aluminate inhibited solution) is a versatile inhibited system, its application reduces the consumption of chemicals and materials, increases the stability of the wall of the near-wellbore zone of the wellbore and increases the relief of the wellbore, bringing it closer to the nominal diameter.

References:

1. Булатов А.И., Пеньков А.И., Проселков Ю.М. Справочник по промывке скважин – М.: Недра, 1984 с.42-57.
2. Временный патент ТМ №387, МПК С09К 7/02, Ингибированный раствор.
3. Патент RU №2136715, МПК С09К 7/02, Способ обработки глинистого раствора комбинированным реагентом.
4. Ограниченный патент ТМ 3503, МПК С09К 8/06, Способ обработки бурового раствора ингибированной комплексной добавкой «КАИР».