Active borehole salt mine at Przyjma near Mogilno, producing brine and hosting a strategic underground natural gas storage facility.
Kopalnia Soli „Mogilno" is an active borehole salt mine located at Przyjma near Mogilno in the Kujawy-Pomerania region of Poland, operated by Inowrocławskie Kopalnie Soli „Solino" S.A., a wholly owned subsidiary of ORLEN S.A. The mine extracts brine from the Zechstein salt diapir by the solution mining method, without underground descent by workers. The Mogilno diapir was identified in 1956 during oil exploration drilling; two salt deposits were subsequently documented, „Mogilno I" (1963–2006) and „Mogilno II" (1981–2007). Construction of the mine began in 1978 and production commenced on 13 February 1986, initially from 16 boreholes, with exploitation beginning at a depth of 1,400 metres.
The mine replaced the closed underground Kopalnia Soli „Solno" in Inowrocław. Brine is piped to Janikowskie Zakłady Sodowe; approximately 130 million cubic metres were produced in the mine's first 35 years. From 1997 the mine's exhausted salt caverns were progressively converted into a strategic underground gas storage facility, Kawernowy Magazyn Gazu Ziemnego Mogilno, with a target capacity of 800 million cubic metres.
The Zechstein salt diapir near Mogilno was first identified in 1956 during petroleum exploration drilling. Further boreholes and geophysical surveys confirmed the presence of two exploitable rock salt deposits: „Mogilno I", documented between 1963 and 2006, and „Mogilno II", documented between 1981 and 2007. The diapir has an elliptical plan measuring approximately 8 × 1 kilometres, with the salt mirror at depths between 210 and 600 metres, overlain by an anhydrite-gypsum-clay cap 100–160 metres thick. It forms part of the Zechstein salt-bearing formation of central Poland, comprising salts from three evaporite cycles: Stassfurt (older salts), Leine (younger salts), and Aller (youngest salts).
The decision to build a borehole salt mine at Przyjma was linked directly to the deteriorating safety situation at the underground Kopalnia Soli „Solno" in Inowrocław, which faced persistent water ingress hazards and was closed in 1986. In 1976 the Minister of the Chemical Industry established the Obszar Górniczy „Palędzie" covering 13,427,836 square metres. Construction of Kopalnia Soli „Mogilno" began in 1978 and was completed in 1986. Production was inaugurated on 13 February 1986.
The mine operates entirely from the surface by the borehole solution method with oil-cap insulation of the cavern roof. Water is injected into the boreholes, dissolving the salt and causing brine to flow to the surface. Miners do not descend underground. Initial production was from 16 boreholes, with brine piped to Janikowskie Zakłady Sodowe. Between 1986 and 2016 the mine delivered approximately 111 million cubic metres of brine to those works. The mine became the successor facility to Kopalnia „Solno" in Inowrocław and the principal brine source for the industrial soda and chemical sector in the region.
From 1997 the mine's function expanded to include underground energy storage. Exhausted salt caverns were progressively converted into Kawernowy Magazyn Gazu Ziemnego Mogilno, a strategic underground natural gas storage facility, with a target storage volume of 800 million cubic metres. The KPMG Mogilno facility is located within the Mogilno salt diapir in Mogilno and Rogowo communes and forms part of the national energy security infrastructure.
In 2016 infrastructure for six new production boreholes was constructed, expanding the mine's extraction capacity. By the time of its 35th anniversary in 2021, approximately 130 million cubic metres of brine had been extracted since production began. The mine continues in active operation as a unit of Inowrocławskie Kopalnie Soli „Solino" S.A., which is wholly owned by ORLEN S.A. and is the largest brine producer in Poland, producing approximately 9 million cubic metres per year across its two operating borehole mines at Przyjma (Mogilno) and Góra near Inowrocław.